This is some very strange logic here. It's so odd that I feel like doing some point-by-point rebuttals.

> Commissions are all well and good, but they don’t pay very well and there’s a physical limit on how many a single person can do.

Which is why the creator of a creative work might be okay with something like that.

> The merchandise I had in mind was buttons and stickers and prints and other physical incarnations of art. You see this kind of stuff sold rather a lot at anime conventions

Which is precisely why it's not okay. You're not adding anything of your own, you're just profiting off of someone else's stuff.

Here's the question you should be asking: are you making a profit from something you did not create? If so, that money is not yours, you did not earn that money. You didn't make the video game, the story, the art.

> Copyright was originally invented for books.

While true, that's only because books were the first mass-produced creative works. By the time the US constitution came around (and the copyright clause in it), the concept had been well extended beyond that, even to the point where the idea had been generalized to technology andn scientific discoveries (in the form of patents).

> Fan work is created from scratch. It’s new.

No, it is a "derivative work." Putting someone else's pictures given meaning by a game they created onto a button and selling it is not a "new" work. If it weren't, why not just leave out the stuff you didn't create and sell it on your own? You can't, that's why.

> Gatekeeping

This is a really idiotic excuse. Steam isn't the one telling you that you can't sell other people's art and taking all the money for yourself, the people who made the art are telling you that.

> When copyright was introduced, “creators” were a sort of elite. You had to have a lot of equipment and resources, or more likely, you had to attract the attention of someone who had a lot of equipment and resources.

More self-serving rationalizations. Writing only takes talent and some time. Whether or not it was good enough to make copies of and sell is another thing. Copyright was set up so that anyone could afford it if they were even a little bit serious. Copyright protects the little guy against a bigger person with more resources at their disposal to copy your idea and make a profit off it. It gives them the right to their work because they're the ones that created it.

> Abuse

This section is completely irrelevant. The problems we have with our copyright and patent laws has nothing to do with protecting a small, indie developer, who made a legitimately good game, from being outcompeted by enterprising salesman who are trying to sell merchandising of someone else's work. When did people like Undertale become "multinational corporations"? You can't make someone seem like a faceless and souless being that it's okay to ripoff when you linked to their Twitter account earlier in the article.

It's people like the author of this article that copyright laws are rightfully meant to protect content-creators from - people who can argue themselves in circles to not feel bad about ripping people off because they think putting someone else's game logo on a button is an "entirely new" work.