Because you are outnumbered, basically. You have to make a stand or this problem won't ever go away.

http://news.ycombinator.com/item?id=4187333

Because a convention which many people consider harmless is causing you harm. Using 'he' when gender isn't known is not a tech-specific phenomenon.

Because that way they don't have to take responsibility for their actions.

Also note that their proposed solution doesn't solve anything; it might just prevent you, personally, from being able to complain about it. I'm guessing that is their actual goal.