SeaRabbit, prostitutes are not looked down on because they're committing a crime though are they? They're looked down upon because they are prostitutes. Women are looked down upon anyway, women who have a lot of sex are viewed worse, then these ones are available for any sex at a price, that's why they're looked down upon. Decriminalisation will not change that in the slightest. If anything it will 'justify' those buying sex and give them a green light to behave in worse ways still towards this sub-group and women in general.
As is traditional on these threads, against criticism of the Nordic model, I give you... the complete mess that is the German decriminalisation, with women trafficked freely and treated appallingly.