an avatar is the simple representation of who you are. you dont spend time on the net (or even in real life) to get to know people you randomly see. and why should you?
yes, avatars give you an instant judgment of what you can expect from that person, whether you want to or not you all do it.
if you crop out some gif clip from some cigarettegy cartoon, and caption it with a very old and unfunny meme; it means you want people to instantly think you are some immature fad chasing child. instant loss in respect.