I have never made but one prayer to God, a very short one: "O Lord make my enemies ridiculous." And God granted it. --Voltaire
I only play Eldar/Harlies. I will not give up the army I have played since 1990/1991 just because of other people's opinions ( *air quotes* facts). So every time Eldar rise in power, I tend to get crap until I kindly point out that it is the only army I have played since before some of the people I have played against were born. They quickly quiet down at that point.
And because I enjoy the army, if I am tending to ROLFStomp people, I try to mix it up. 2 weeks ago, I played a 500 point guardian host... and I got destroyed. The only reason it was "close" was because we were doing a maelstrom game. But it was an experiment and I had fun because I enjoy the army and the story behind it.
TL;DR - Play what you want, others be damned =)