I agree, we were just talking about Cell and I was trying to tie it into Frieza as that example is more relevant to his personality.
Well, being too nice is another story. It came back to bite him more than once with Frieza. First not quickly letting him die not only wasted his energy, he then nearly got attacked by King Cold, and then Frieza's brother(twice, due to two moves).
However, him saving Vegeta more or less helped the world overall. Albeit, you could easily argue that outside of Trunks himself existing(and coming back from the future), Vegeta pretty much ruined everything. He was not needed during the Namek saga and Goku could've easily taken care of stuff(or somebody else could) that Vegeta tried to do. The Saiyan Prince was useless against Frieza. More notably, he's the main reason why Cell was able to reach his perfect form. And that's actually as far as I was able to see. I never saw beyond the Cell saga, sadly. I hope DBZ Kai finally finishes the full series off.
I honestly did like him a lot more in GT, which, to be honest, I found was a nice addition to the series. Having a fully fighting female(for the whole series. Until the Cell saga started, we had no one. Bulma and Chi Chi hardly count, despite clearly being pretty strong characters overall. I actually would not want to be Cell if Chi Chi was nearby... especially if he threatened Gohan. Hoo boy... Albeit, Cell would likely win, but hot damn, would she have likely at least dealt some severe damage. Obviously not against Perfect Cell, but his earlier forms, well... I doubt he'd even be able to absorb Chi Chi as well. Unlike Buu who did beat Chi Chi by metamorphisizing her into candy, if I remember correctly, Cell doesn't have such abilities. Also, if he had hurt Chi Chi, let's just say that dealing with a mad Goku and Gohan would've made him beyond toast. As for Bulma, she's kind of meh fighting-wise, but clearly has Vegeta on a leash) was very nice in itself, plus, a female Saiyan existing was a really good move too.