It's not about being nice. It's about being thoughtless. Snow says he'll do it, but he has no plan, no idea how to make it work and doesn't even attempt to think about hit. He just goes in, forcing his way, hoping one thing just clicks along the way. The reason I dislike him so much is that he just doesn't stop and think even for a second, which really is what a normal person would do when the stakes are so high.
Vanille I'm just meh about since she's just bland and clearly only there for the fanservice.
And for the record, I love nice characters (heck, being nice was like the biggest characteristic of my last RP character) and I think people are way too often mistaking "rounded, three dimensional, and strong" for "basically a huge dick". But I want my characters to feel real first, and if they're real and nice, that's awesome. If they're m real and bitchy, that's okay, but if they're fake and either nice or bitchy, then all they get from me is a groan. It's all in the writing and if they're not in your face and I can understand where they're coming from with their niceness/bitchiness, I will like them as a character, even if I wouldn't like them as a human being.