It makes you a casual gamer and that's all sorts of bad.

Nothing is wrong with. I actually used to look down at people who did it but now I do it too.

I have never noticed difficulty snobs. Me personally I tend to play my games on the hardest difficulty setting.

There are certain genres where I suck, so I tend to play them on easy just because otherwise it would be nearly impossible for me to go through them. For the rest of the games, I'm still bad but I can play them on normal, some of them on hard on my 2nd playthrough.

I play for the fun, not for a challenge.

Nothing is wrong with it as long as you're having fun. The only reason I don't do it is because the game is over too soon and I don't feel like I get enough gameplay out of whatever it is I'm playing. This is why I love achievements and trophies so much. My games last alot longer.

I usually play on normal for the same reasons you do easy mode.

Replaying levels or part of levels is just a waste of my time that I could much better use to play games from my backlog (or do something else entirely).

It's troll bait.

Manly things.

Common complaints such as too short or bad ai can be diminished via higher difficulty settings and then there are some games that REALLY come alive with the higher difficulty settings, such as Halo, Hitman, Splinter Cell (original trilogy) and Timesplitters 1 & 2.

Games that are not very dynamic (or basically played on autopilot) like COD, Uncharted or Battlefield games makes no difference whatever the difficulty is. There is no need to play on anything above easy on such games and the difficulty does not change the gameplay by a single ounce. 

Nothing at all. If you enjoy a challenge, raise the difficulty. That's about the only thing. People don't like when they worked hard to earn the right to see a story in a game and then seeing people (in their eyes) cheat their way through by playing on easy. At least that's what I think the reason is for a lot of it.

I mostly play on Normal myself, I never play on hard unless there is a trophy involved. Like Infamous or Last of Us.

There are lot of games that play quite different when you play on easy, especially one with good AI coding - I always bring up FarCry 1 as example which on hardest difficulty has specially clever AI, while on easy it's pretty much cakewalk.

That said, I don't think there's anything wrong with playing on easy per se - for example, my brother plays all his games on easy, and I've never mocked him for it - in all 30-35 years we've been gaming, he was never really good at it, and honestly never cared to be anything but casual gamer.