Douk said:
"you need to dedicate an absurdly long time to learn to play"
"smash bros is the best fighter because it is easy to play"
"all the good players are conceited nerds"
"being good at the game makes you less of a person than I am- I have a life!"
These complaints (which is all but one of the complaints you listed) come from a basic competitive principle that is intensified by a number of factors to the point where many people just don't have fun.
First off, in any from of competitive game, you will always have some people who play the game a lot, learn the game in and out, and if they go up against someone with considerably less skill, the less skilled player will be trounced. This is true of all competitive games (and not just video games).
This experienced-trumps-beginner principle is intensified when the mechanics are not simple. Games with mechanics and skill sets that can be learned and developed quickly are more welcome to outsiders than games that really require familiarity with the fine-tuning of the game, the competitor's play style, and the physical skills that require practice to become normal.
This experienced-trumps-beginner principle is intensified in one-on-one scenarios. In bigger games with multiple players, whether team-based or free-for-all, there is a constantly shifting dynamic where the the beginner is not always besought by the most experienced player. There is also usually a dynamic in the environment, which can give a player an advantage based on his position relative to another player.
This experienced-trumps-beginner principle is intensified when stats/equipment/abilities don't change mid-battle. Games that feature weapon changing, pick-ups, or special bonuses in the middle of a battle introduce another dynamic by which the beginner MIGHT have a chance a chance against the veteran, or at least, even if the veteran dominates the scoreboard, the beginner might be able to pick up a point here or there.
Basically, there are fewer ways around "experienced-beats-beginner" principle in a lot of fighting games. Yes, there are some fighting games, like Smash Bros, that try to get around this by having simple controls, more than two players at a time, and things like environmental shifts and pick-ups to give less experienced players a possible advantage. That's why it tends to be more well-liked among non-fighting game fans.
But in general, fighting games, by their very nature, tend to breed competitive communities that aren't particularly welcoming to those who aren't willing put in the time and effort to become an experienced player, and the kinds of comments you list are probably from people who have felt shunned by said communities.