alt Hacker NewsThe fact that someone actively worked against the welfare of society as a whole, in significant and impactful ways, _is_ a criticism of their credibility. It speaks to their morals and empathy for others.
It doesn't mean that what they're saying is a lie, but it puts them firmly in the bucket where what they say needs to be verified.
It doesn't matter if she's as bad as the others. The message is that the others are bad. Pointing out that she's also bad is meek at best.