don’t knock it until you’ve tried it? :\?

I was just wondering if anyone else had a problem with this phrase.
Firstly I dislike it because it assumes you have to experience something first hand to have any opinion or ability to foresee any possible consequences.
I secondly dislike it because if you stick to your original stance then everyone will call you a hypocrite. (agree/disagree?)
Like, for example I may have a problem with certain illicit substances like hard drugs or maybe prostitution etc.
I think at times it’s best to have a negative perception of something that is potentially dangerous without actually knowing it for yourself. I may enjoy the effects of crystal meth if I try it but I know there is a possibility of addiction and both health and legal issues down the road in the long run. So from an outside perspective I think it’s acceptable to say that it’s not a good idea. As for prostitution,is it so wrong to have personal standards without experiencing a perception of self degradation? Just because you’ve done something once shouldn’t automatically make if fine for everyone to do all the time (imo) but that seems to be the entrapment of “don’t knock it until you’ve tried it” for fear of looking hypocritical the previous standards are abolished.