People like to see negative attack ads on opponents that they do not like. It makes them feel more vindicated on their positions. Voters welcome these things because it allows them to not take the time to figure out who the best candidate is based on facts or political opinions.
I think all ads should be okay. politics is all about who is the best liar. If someone is held back because they can't release certain information that they think is vital to their campaign, i think it is unfair if they can't be able to release anything, not fair at all.