You just demonstrated exactly what the comment was trying to express. Perfection.
And both things are true. Both parties do various bad things, and their supporters hide behind the "well the other guy is bad too!" argument. The best candidate is the one who has the lowest expected badness; and yes, their chosen party membership is a valid and at least somewhat-informative prior on badness, depending on your personal badness disutility function.
The amusing thing is that I genuinely do not know which side you mean to refer to here. I guess it really does prove the point above.