Well, first off, it is really annoying. All you do when you reply to a spam topic, is bump it. Now if there is bad material in that topic, your allowing more people to see it.
Second off, it's not a members right, to post stuff like that in a topic, there is such a thing as privacy.
Third off, once you've reported, the person is well aware that you've reported them, if they stay on here. Bots won't reply back, or even look over replys, and most spammers get on, post one message, and get off.
An lastly, once you post in their post it's counted as flamming/trolling/spam, depending on what you wrote, and then YOU can get in trouble.
Just saying.