We don't have a lot of social cues to go on on the Internet so a lot gets read into simple things a lot of times. You can see lots of examples of that on this very forum. When you come out and say "I want to take it slow" it could very easily come off as "I'm a prude." It's not that you want to take it slow so much as that you came out and said it right away. the other person knows so little about you at this point that everything you say becomes a primary indicator to your personality. The fact that you brought up taking it slow in (presumably) your very first message to him indicates that you may be a waste of time. After all, he doesn't even know you yet. When one of the first things he knows about you is that you want to "take it slow" it seems like there may not be a lot of return on investment in this deal.