Well, parenting is a old profession (although, you don't get paid for it
) but Technology like computers are very very new.
I'd have to say that Monitor software is a combination of both good parenting and invasion of privacy.
It's a good parenting b/c you don't want your children, especially teenagers to access materials that are somewhat questionable (porno, illegal downloads, chatting about questionable topics, etc).
When it comes to privacy in chatrooms, it's pretty hard to define a fine line between what's good to talk about and what isn't good. I tend to view chatting with people online is the same as talking to your friends in person or on the phone.
The reality is this: It's YOUR computer in YOUR house and it's just as the same if your stepson is talking to his friend in your house. It's up to you how your stepson should conduct himself, especially in your own home.