It may sound either harsh or naive, but seriously my only strategy right now is to just hope that people using the service don't feel that way. If I understand your point, I personally (or someone working for the service) would have to start trying to recruit people by (a) getting big lists of known emails (easy to do), and (b) sending them fake messages that (for example) someone is interested in dating them.

So I guess I just have to keep my morality in check? :)