I think every single person in the world has the right to remix, cover, or mash up any song in the world.
Don't put a limitation on a person's creativity. Who cares if they mix a song you like? They're not somehow eliminating the original, so you have nothing to worry about.
Sometimes - I find it quite interesting when there are different versions and it's quite cool to see how it's been changed - I usually end up liking them all for different things
In my opinion, it can go a lot of ways. The classic Beatles song "With A Little Help From My Friends" was covered by Joe Cocker, and it turned out brilliant. But the Glee cast made, in my opinion, horrible Beatles covers. I do think people have a right to at least give it a try, even if they might crash and burn.