i don't know if this is the reason everyone hates snow but the reason i can't stand him is because he reminds me of my douchiness when i was 15ish.
I think those are both part of it. He's supposed to be what, over 20 (?), and acts like a stupid 14 year old, and he's just so "shounen hero" in his entire belief system (if you can call it that).Snow, if taken a little further, honestly could've been like a parody of the typical JRPG hero. Square gets shit for its' moody heroes but I'll take them over the average JRPG hero that believes in the power of friendship, hope, and rainbows.
I liked Sazh, Fang, Lightning, and even Vanille later in the game, and I can deal with Hope as a character who is, well, necessary to some degree. But Snow, I just hate his guts.
Even though a lot of JRPGs, anime and also lots of western media targeted at teenagers doesn't always show it, there is a huge sea of possible characters between "brooding gothic emo" and "happy friendship-powered hero". /rantbut that's what makes them good, not everybody needs to be gritty gothic type with dark past, you know.