This was a big topic a while back when I was attending comic conventions. There is a tipping point where something is helping to generate notoriety for a property by fans of it and where it's generating profit for someone who didn't spend the time and effort to create said property.
Like if I saw someone doing commissions or fan art with my characters at a convention, no problem. Comic aggrigators are usually free advertising, and don't usually last too long anyhow. But production-lining prints, shirts, etc... not cool.
If you profit from somebody else work, they deserve a percentage for creating it. That's the crux of copyright law. If someone came and at least asked for permission, you could work something out. For many artists, who have devoted a large chunk of their life to their craft, that property (or deal to use a character from a publisher they worked for) may be their only hope for income in the future.
What would I do, I don't know. But if someone else was profiting off my work while I struggled to make a living, I'd feel pretty hurt by it.