I generally ask:
Do they/have they done it?
If its so great why are girl children being trafficked into it, and why aren't men queuing up to do it?
Would they be cool with their daughter/sister/mum/granny going on the game?
Do they know the rate of addiction in sex workers?
Are they aware of the stats of sex workers being murdered, raped, assaulted or robbed at work (and the same stats for someone say working in a McDonalds)?
Have they ever witnessed a pimp going at one of 'his girls' in the street?
Did they watch Pretty Woman as a young person and know f-all about the reality of sex workers lives?