Great sentence. In that case, it means that this person is really, really, extremely good-looking. So good-looking, in fact, that the person's beauty could cause damage. If I had to guess, I would say that this expression goes back to Helen of Troy, who was so beautiful that the Trojan War was fought because of her beauty. As for 'wholesome', it is just a compliment about someone's character usually, but when applied to beauty, I would say that the person doesn't have plastic surgery, doesn't wear much makeup, etc. Basically, their beauty is all-natural. "Does them in" typically means "kills", but in this case it's being used to say that this person, the handsome/beautiful person, gets whatever they want because people are weak to really good-looking people. This is an over-the-top, very flattering compliment, that's all. It uses exaggeration to say, basically, that this person is good-looking.