I should note, that the typical responses like "but what about potentially contracting a STD? Isn't that harm?" isn't really a rebuttal because of reason #2. If you're consenting to sex, you're consenting to the potential risk it presents. That's why, I, personally, wouldn't shack up with someone I just met. But, I'm not going to judge what another does with their body. If you don't have ownership of your own body, what do you have ownership of?
"I was thirsty for everything, but blood wasn't my style" - Live, "Voodoo Lady"