Because quite frankly I find it slightly sinister. I am annoyed at Old boys' clubbishness of it all. Why shouldn't people write exactly what they want to on their first post? Or second or third? Is there some unwritten rule that says you're not supposed to be too controversial or opinionated on your first posting?
And no I'm not referring to any one particular response to any one particular thread-it's just something I've noticed come up a lot it's almost a cliché. So next time you feel compelled to write 'interesting first post' to anyone, please reflect on what you actually mean by it. And then say something a bit more original. That's all I have to say on the matter, and a very good evening.