I've had a couple stream Mods alter titles of my memes to troll me. It's annoying, but not all that important at the end of the day.
I Mod several streams myself. So far I've found no reason to ever alter the meme title of anyone else's submissions. I would reserve the right do it if the title were something offensive, vulgar, or just not in line with the terms of the stream. But if that were ever the case, typically the offending content would be apparent in the meme itself rather than just the title.
I do appreciate how ImgFlip generally empowers Stream Mods to control their streams' content and viewpoint. It's a good idea to allow broad powers, since Stream Mods have the best idea of what they want their streams to look like. It also takes work off of the Community Mods' and Global Mods' plates.
At the end of the day, folks who aren't happy with a Mod's actions can always complain -- assuming the Stream Mod listens and permits it! -- or, ultimately, just take their content to a different stream.
Stream Mods who make wise decisions, feature interesting content, and appropriately control harassment and trolling will see their streams flourish. Stream Mods who take unwise actions and piss everybody off will soon find their streams to be lacking for new submissions.
That's free speech and the free market in action.
Empower creativity and let a thousand streams bloom.