Stand up for yourself, but try not to hurt people's feelings. When you communicate electronically, all you see is a computer screen. And that goes for your correspondent as well. And it's frighteningly easy to forget that your correspondent is a person with feelings more or less like your own. It's ironic, really.
Computer networks bring people together who'd otherwise never meet.
Most of them would never act that way at work or at home. But the interposition of the machine seems to make it acceptable. The message of Netiquette is that it's not acceptable. Yes, use your network connections to express yourself freely, explore strange new worlds, and boldly go where you've never gone before. Those are real people out there.