I think it may be true that some people play easy classes because they can't play hard classes. But sometimes people play easy classes because they don't want to work hard all the time. Playing a challenging class has its rewards that you can't get from playing an easy class, that's true. But sometimes people get home from work or school and they just want to unwind a bit, and there's nothing wrong with running around going pew pew pew for a while. Not everything one does in game has to be super serious competitive hard work.
For that reason I think it's unfair and short-sighted to lump everyone who ever plays a FotM class together as a skill-less scrub who can't hang with the big boys. I think that's an expression of an inner frustration; Why are those guys having fun when I'm working so hard? Maybe relax and unwind a bit and try it yourself. Sure you can say that that sort of play doesn't remain interesting because it isn't challenging, but watching TV isn't challenging either yet it's still the number one form of entertainment because sometimes that's what you need.
It's the people who exclusively play easy classes, and then act as if they have accomplished something challenging, that we should direct our scorn towards. Even if I think it's fine for someone to run around blowing things up on an easy class, they should still recognize that that's what they're doing. No one likes a person who tries to inflate their own ego, especially by kicking around other people.