And the truth about a problem is something can be around for awhile, but when the right people decide the make a big deal of a problem it can explode.
You can have it where in a very short time the population can go from neutral to uneasy relationship with each other to where certain people start fanning the flame to increase the fear and distrust of another in its population, therefore increasing fear and distrust by revealing the problem and it works all the time, because people in general as a group can be fickle, fearful and easy to manipulate.
In the MCU world, all you need is for someone on a news channel to say 50% of superpowered based violent crime is done by mutants. Not all mutants are bad, but most of these crimes are done by them compared to 25% Inhumans and 15% other alien origin and 10% Humans who gained powers by experiment, accident or on their own technology.
And even in real life, that would get people going, even if before they were bombarded by news like that when they were possibly neutral or Leary of Mutants, afterwards they would be more leary of them that a human like Stark or even Spider-man.