You are wrong here. If you download a free demo on steam it will automatically removed from your library whenever you uninstall it. They simply treat demos different then full games and as I said technically I doubt there would not be a problem to do this here as well. Please don't get me wrong: a free demo is always something good so I am glad that GOG offers them to us - I am just saying that there would be room for improvement how to do this - that is all :)

If you uninstall ANY free game (demo or not), Steam will remove it from your library.

That's really not the right way to do it.
In fact, as much as I like GOG, I think this demo system thing is below any standards.

First of all, why do you need to go through a process which is similar to buying a game if you only want to try a demo? A simple download link would be more than enough. If you want to make sure no one abuses that link, make sure it is visible to only registered users. If I need to go through a checkout of sorts and then try to find the demo in the account page, I much rather choose not to try it at all. (Although in this case I have the game anyway, as a backer, but that's not the point.)

And in case it's a game I really hate for whatever reason, it stays in my account for all time to come, unless I contact support for something as trivial as not liking a demo and wanting to get rid of it? Riiight...

If downloading game demos was a simple process 20 years ago, making it more complicated in this day and age is really counterproductive.

Not only that, but having the demos on their own game pages is a really bad idea. Someone who is browsing through games, and finds a game page of an interesting game, should have the download link easily available on the game page. Now, there is only some strange "Buy series – complete it" thing on the right side of the screen with absolutely no clear indication that
1) it's a game demo
2) it's free.

"Buy series – complete it" would indicate that you need to pay for some product, so finding a free demo which is not necessarily so much a part of the series but rather a sample of the game goes against any intuitive user experiences that I am aware of.

And like said, if someone actually clicks that link, that person would need to go through all that trouble just to try it out.

Having demos is a nice idea, but if you don't do that properly, then you probably shouldn't do it at all.

nice, ill give it a go and see, love the ability to take a game for a spin before buying. thanks!

I would take this one step further: I think it would be enough for GOG to simply link to a DRM-free demo hosted elsewhere (which should be the developer's or publisher's site, usually), rather than them having to do everything they normally do for a full game (testing and packaging, offering technical support, trying to keep both the product and their package up-to-date) for something that they'll not directly profit from. It's one thing if the developer doesn't host their own demos, and only puts them on Steam or itch or whatever, but I'm pretty sure some of the demos that GOG carries are also available straight from the developers.
It's a nice idea to offer them on-site as well, but if their version is redundant, it's also kind of pointless.
(And, to be clear: I, personally, have zero problem with having to go through the checkout for a free item.)

But it is totally a good idea for them to not have any way for items to be deleted permanently from a user's library from within that account, since it could easily lead to account thieves (or the account owner's children, or an angry s.o. or ex, or...) maliciously deleting things. GOG doesn't want to have to have their small support staff to have to deal with the aftermath of such messes, so they require the user to go through Support to delete things in the first place.
It would be cool if they would differentiate between paid items and indefinitely available free items, where you could delete the latter on your own, but not the former; but changing their software to be able to do this would also almost certainly require a ton of extra work for the site developers, and for very little benefit to the majority of users (for whom the "hide" option is enough).

EDIT: Rewordin' & typo fixin'

GOG: "Hello, we're hosting a demo for you!"

Goglins: "WHY DON'T YOU ALWAYS DO THIS AND BTW YOU'RE DOING IT WRONG1elventyone1!1"

The hell of it is, before they started carrying demos, I saw a few people idly wishing that they would carry demos, but I don't remember that being one of the things that people really complained about them lacking, let alone demanding that they start adding. Yet, now that they've started, they'll get unceasing complaints about how it's done, and if they were to stop adding new ones, the ingrates and malcontents would be climbing over one another to rip GOG a new asshole and moan about how they've been "betrayed".

Those opinions don't cancel each other in any way.
It is a good thing to have demos around so that you can try before you buy. Especially this would be beneficial for older games, when the original publishers are no longer in business and there's no official channel to get those demos anymore.

But there can be right ways and wrong ways of doing things. And the way GOG is doing their demos now is a wrong thing to do.

Let's imagine a situation where GOG would one day have 200 demos in their catalogue. The way they distribute these demos would mean that there is also 200 extra game entries, which aren't really games but demos. But if you were to sort the catalogue by genre or something these demos would clutter the search results, unless they add some "include/exclude demos" search option.

Even if that existed, the underlying problem still remains. If someone were to try, let's say, 50 demos, that person would have to go through the checkout and account and download process 50 times. And if none of those games were to his liking, and he wants to keep his account "clean", he would have to contact support 50 times just to have those deleted.

The amount of needless processing on the server side and unproductive human work would add up to ridiculous amounts if there's more customers going through all that.

Now compare that with how demos have traditionally been distributed: click to download, uninstall to get rid of for good.
Additional serverload: minimum, only what it takes to handle the file transfers.
Additional human workload: none.

Maybe it's my background or whatever, but I have been taught to
1) minimize the needs for computing power
2) minimize the human involvement
3) maximize the user friendliness.

The way this GOG demo thing works goes against all three. If they are happy with it, if most of the customers are happy with, fine. That still doesn't mean it's a clever or good design. And from a customer perspective, I personally won't be using it. But that's only my personal opinion, I can be wrong and completely lost on this.

Demos are always free, so why GOG overstates this? I don't understand.

What I'm wondering is why they capitalized "demo". :?

Well back in the day you actually had to pay for demo disks sometimes. Although when it comes to Internet distribution, I can't recall seeing a game demo that wasn't free. Unless alpha builds count as demos, of course, but as far as real demos go, I think they are free in practically every case.

Not the way I do remember my words

"so I am glad that GOG offers them to us - I am just saying that there would be room for improvement how to do this - that is all :)"

Don't see anything wrong in mentioning this.