What's more, the original idea of the X-Men by Xavier was to have good PR. The X-men costumes were to imitate superheroes and be better accepted by the public.
The X-Men were a vehicle for one purpose: to improve the perception of mutants among humans. They believed that if they were heroes and saved the world, humans would think "Hey, these mutants are good guys, let's stop killing them."
But it didn't happen. They didn't stop killing mutants.