I had a run in with Zazzle the other week where I was trying to buy a Justice (band) shirt and it ordered. I wondered how long it was going to take to ship and checked, the order email was a notification on how they can't make that item due to copyright. Since users can post any design or image for sale, they don't really police it. So, they are very much in the mindset of no complaints means permission. Definitely is uncool for everyone involved.

Basically it's more or less:

"There is so much stuff on there we can't possibly police it. So we stick a line in the TOS that says 'you will not upload anything you don't have permission for" and then wilfully ignore everything our users upload. We will only ever do anything if the real rights holder, themselves (or legal representative) contact us and specifically list each offending item individually."

That's basically how ALL these 'user generated content' sites work.

EDIT: The individual posters don't have enough money to be worth going after (usually). And the sites only get sued if they get large enough (e.g. YouTube) and the suer (is that a word?) has enough content on there worth getting a settlement for (e.g. a record company, or big TV company).

Most rights holders can't be bothered with sending continual DMCA's (only applies in the US anyway), and the sites would whine that it'd be a burden to check the legitimacy of every upload, or to develop a system that'd do it semi-autonomously (like YouTube's ContentID).

In general, most big companies don't try to oppress small-scale fan creations, especially when it isn't using their direct art, though technically, some might be found in court to be infringing. Art/Copyright/Freedom of Speech laws are largely up for interpretation and by a case-by-case basis with a myriad of conflicting precedents. (Though if you're a giant corporation with expensive lawyers, you'll probably win.)

There's plenty of examples in that link you posted of just the straight logo thrown on a shirt, and that's pretty easy to show it's infringing as there was no re-interpretation or alteration. But the vague area begins once you start truly altering or creating your own work/variations with an IP. Where do you draw the line between infringing and freedom of speech? What part of the creation is a reference to something that exists and what percentage is your perspective/expression on it? For example, an anti-corporate painting in a gallery uses the character Ronald MacDonald. Is that illegal if you sell it? Or is that using a common icon in society and culture and expressing a view on it?

More questions: If you create a character named Darkwing that's a duck dressed up like Batman, is it parody or allegory? Is that your own idea or are you actually stealing the idea of Batman? Wasn't Batman a variation of the Shadow and Zorro? On another note, if a shirt jokes about Game of Thrones, is that infringing on that book/show's rights? What about if someone personally commissions me to draw their Guardian - are they paying for the Destiny IP or are they paying for my service?

In many cases, some of these small-scale fan art/creations work in the company's favor. It's marketing and allowing a culture to grow around your IP. It's only when it starts to compete with something the IP is intended to make money off of that you see it shut down. Some contracts with IP-owners also allow for small-run prints and materials using their copyrights. Marvel/DC actually relies on commissions and prints from artists using their characters in a way, as it leads them to find new and popular talent all the time.

So the answer is: It's not. But sometimes it is. And it's all really confusing. But usually it's ultimately up to the IP-owner's discretion and their ability to enforce that discretion.

Anything that is "confusingly similar" to this logo is infringing on Bungie's trademark rights: Destiny TM

Any creation (and I mean any) that is derived from any of Bungie's IP, runs a risk of copyright infringment due to the breadth of their rights in "derivative works".

If you make it and use it personally, you are okay. If you make it and generate any money from it (even website ad revenue), you are infringing.

However, just because they have the rights doesn't mean that they will choose to enforce them. It often will make better business sense to ignore the small fish and avoid any bad press for beating up on your fanbase.