Assuming you are really asking, the two largest objections:

- religious/cultural. My beliefs forbid this, it makes people bad/worse in some hard-to-define way, so no one should be allowed to do it. Sometimes with an emphasis that the sellers are luring good people into sin/ruin.

- it harms women. Many of the participants are trafficked or coerced in some way (and further abused). The profits from the industry encourage more of this. It “warps” the mind of men who use it, leading them to mistreat and abuse women.

I see elements of truth in all these, but IMO they are ultimately not compelling, prohibition is unworkable and unduly infringes on willing participants and consumers.