I have not seen him perform any outright evil acts. The worst thing he does, is joke about Vision dying again.
But he also cares about the kids and enjoys spending time with them. He also listens to Wanda, when she tells him about her grief.
Well, of course not. He didn’t come to be
outright evil; the totality of his actions are
subtly evil – his every interaction with the kids is well-summed up in his own words: “Raise hell, demon-spawn!”
His every interaction with Vision serves to divide him from Wanda (even replace him as a father-figure — Pietro’s words, not mine). His counseling of Wanda validates her actions and comforts her, but without true empathy, as shown when he says the thing that gets him blasted.
Two other things worth looking at: the telepathic kid thinks he’s a vampire and is afraid of him. And this Pietro says he was shot like a chump – which is a weird thing to say about someone who sacrificed his life to save another.
Okay, one more, addressing the idea this Pietro might be the one from the Fox movies: Fox X-Men Quicksilver is so much faster than bullets that he can rearrange them in flight. That Pietro didn’t get shot like a chump in the street. At least not from the front, like the corpse suggests (and like Age of Ultron Pietro did).
[Edit to clarify: With regard to Pietro’s relationship with the kids (as a replacement father-figure), he is a consistent corrupting influence. He isn’t shown steering them away from mischief once. Always toward. Always at the expense of others.]