It's a bit difficult to have an adult conversation with a reddit-fedora brain, but I've done worse so let's go...
It's always amusing to see the progressive crowd pretend not to be motivated entirely by religious beliefs. Even the simple notion that human individuality or self-expression mean anything at all in the universe (rather than being purely epiphenoma, that we can freely suppress or destroy as needed to achieve broader goals) does not come from anything in the natural world or sciences, but entirely from the intellectual & moral inheritance of religious thinking that establishes the person as a locus of essential, transcendent value. The natural world teaches nothing but brutality of the powerful over the weak, & even rape as legitimate ways for stronger beings to succeed and spread. Be honest about the origin of your beliefs; even back in Plato & Aristotle, the organizing tenet which cannot be removed from their elevation of ethics is a thoroughgoing theistic conception of the universe.
More on point: sex is the most critical centerpiece of ethical systems in every single civilization on earth for quite rational reasons. It's the only human activity which creates new human beings--whether consciously intended or not--and therefore should always have equal centrality under the law as acts of murder or destroying human beings; they are symmetrical ends of all human morality.
Prohibitions of various kinds against unfettered sexual activity have everything to do with basic social order, ensuring children are given due weight and that their biological parents are mostly united (we live in the world possible era today on this point, unsurprisingly), and ensuring that the strong & attractive don't totally overpower the weak. That last point is particularly salient today: the distorted sexual marketplace simply means that the attractive and wealthy, who can weather the market, run off with the benefit, while an increasingly massive portion of the population remains alone. But that's another topic about the reality of sexual economy and the way that "liberalized" systems simply throw most ordinary people to the wolves or shrug at their solitary lives.
This is highly disputed and debated, by no means some kind of clear and universal finding, I'm sorry to tell you. First of all Holland was not a typical case; in its prior situation, before brothels were legalized, it had an unusually rampant economy of sex for sale, due to a generalized decriminalization strategy going way back which created a pretty terrible hotbed compared to most civilized nations. It's a bit like letting cartels run amok for a century and then legalizing all hard drugs one day, then claiming that this argues against avoiding the proliferation of destructive drugs in general; no, it obviously doesn't.