If people ask politely (or at least, aren't acting like jerks) I'll tell them what I'm doing and how, and if they ask why, I just tell them that it's fun. People who try to be abusive are quickly ignored (not with the /ignore function, I just stop responding to them). So far I've run into few people who even bother to ask me anything, much less be a pain, but this is partly by design- I run instances almost all the time and at off-hours. So I don't run into many people at all.

As for costs, well sorry... I'm not 15 years old. Mommy and daddy don't pay my way. I pay more than twice as much for cable service as I do for 5 accounts. I pay more when I go out one or two weekends a month than I do for 5 accounts. If you've got a decent job, low debt, and few other expenses, it's just not an issue. Sure, for a schoolkid or someone who is struggling to make ends meet, it can seem like an extravagant waste (and I know enough about struggling to make ends meet!).