I think men need to be aware a backfiring proposition might end up making the women in question fearful that her negative response might damage her business prospects. Leaving a woman feeling like that, or risking leaving a woman feeling like that *is deeply unprofessional and unfair.*
Having said that: as with chat-up lines, this kind of thing has little to do with the quality of the line and everything to do with the quality of the man delivering it. I suspect Scoble's biggest crime was being overweight and unattractive as he propositioned the women in question. Yer, yer, even if you are attractive and read signals well, it's unprofessional, but at the same time as being "a professional," we are all (or at least almost all of us) sexually charged human beings; and when hasn't a bit of risk added to the frisson? Poor Scoble is probably so desperate he can't distinguish "come on" from "fuck off."