If men are criminalised for buying, it may have a deterrent effect, but it would depend on how strictly it were inforced. FGM is illegal in the UK isn't it, but doesn't stop it from happening.
Really, fundamentally I think selling sex is damaging and buying sex us damaging to people. To our emotions, and our path through life.
If I look back to my 17yo self, troubled and desperately in need of cash, I walked into the massage parlour asking for work, I got it, made more cash than I thought I would, and really I've done sex work ever since taking a year or so off now and then. If that option were not available, I'm not sure what I'd have done.
Coming out with £300 after a 10hour day as a 17 year old was a huge "achievement" in my eyes. I was so proud of myself.
If I could only find a job in a cafe or whatever because the parlours had all closed down, maybe I would have done that instead. Claimed benefits, whatever. Who knows, maybe that would have been a good thing?
If we introduced the Nordic model, demand drops, then maybe the people who can't find work here will move abroad elsewhere, and my client base would drop a bit, but it's not going to stop men paying for sex. I'm certain NM pushes it all further underground, increases stigma/fear and causes more pressure to be "discreet", secretive and silent, in order to protect your clients.
Decriminalization makes some sense, and still doesn't make is all "Perfectly OK". A civil offense is committed instead, for those related activities now listed as criminal.