It's like saying we can't say Frieza is an evil person because we don't know for sure that he wasn't donating all the profits from the PTO to puppy orphanages. I'm sure that's not what either you or Terrabrand meant and it feels like a strawman even to me, but I don't know of any other way to interpret what your posts said.
Given his overall conduct, I don't feel bragging is accurate.
Otherwise, I will limit myself to saying that my point, personally, can be summed up as 'this is our first meeting with him and we had limited rumors alone to work off previously'. We know he killed kids, yes. We don't really know how he
conducted himself then or any of what he did prior or hence.
Whereas we knew even before we met him, so to speak, in canon, that Frieza was a galactic tyrant. We learned very early of his annihilation of the Saiyan homeworld. He was unendingly cruel from the first moment he came on screen. There is a minute chance in the early scenes he was 'not so bad', and then he tries to take advantage of Goku's kindness to blow up the world, as i recall.
In short, I'm saying we have too little evidence and too much room, especially now that we've seen him, for the assumptions of guilt on Yammar to be... Exxagerated, and him A Good Man 99% of the time. We, for example, had no clue he was a member of the ancestor cult. Wat other defining features might we be unaware of?
Put another way, he is perhaps more likely than not to be Evil, but it's a 75%/25% kinda divide, not 99+% likely evil.