This is in fact exactly what happens, just consider the ANC in South Africa, US politics or like literally every conservative party in Europe ever.
Which is why any politician is harmful to democracy that primarily competes with non-policy arguments, appeals to tradition/emotion/faith or similar, and any such appeal or argument is a bit of a red flag for the politician in question (to me, but trying to be objective about things).
Alas, no. By and large, people don't vote for policies that are good for them.
People vote for policies that sound good. By and large, they don't really care too much about whether the policy sounds good specifically for them---they are happy to think of eg their country or community. But they are really bad at judging what policies actually work.
So to use your phrasing:
Every vote you get with non-policy arguments means you can make fractionally fewer policies constrained by having to keep promises for bad policies.
See https://en.wikipedia.org/wiki/The_Myth_of_the_Rational_Voter for more background on the argument. (I don't expect my very brief sketch to convince anyone.)
What? How does the conclusion follow from the premise? That a politician resorts to ad hominem fallacies does not by itself mean that whoever listens to them will act purely on those fallacies over everything else. Moreover, the voters are just as likely to vote based on similar fallacies that they come up with themselves. "Oh, I don't like that guy, he has a bent nose." Ultimately it's each voter's responsibility to judge the candidates based on appropriate metric and not be swayed by bullshit, whether of their own creation or not.