Okay, now this is a bit confusing. You don't consider rights and laws to be synonymous, but now it's also not a moral connection?
What exactly is a right? If the animal does not have a right to avoid unnecessary suffering, what makes it immoral?
Why they are or aren't is simple, because whatever the ruling legislative body is, decided to make it a law.
I assume you meant what should or should not be a law, and in that case I think the general guiding principle is that things that have a negative effect on the society, which results in people uninvolved in the act having a reduced level of human flourishing, are things that we should make illegal. Murder is a pretty obvious one. Driving over the speed limit is less obvious, however the in arguable correlation with accident severity makes for an acceptable argument.
Drug use is another great example, and one where the libertarians start crashing into the limitations of their own philosophy, mostly because libertarians have the luxury of not living around drug addicts. Do what you want with your own body starts to fall apart when the drug you are taking causes psychotic outbreaks that end with bystanders being hurt or killed. Punishing the drug user after the fact does little to help the person who was killed her their family. On secondary level, accepting that we have chosen to live in a society that provides services for those who are most in need, allowing people to take a drug that will overwhelmingly put them in a position of need is a threat to the solvency of that system. Thus drug laws.
Prostitution is yet another area where those in favor of legalization have seldom had any direct experience with actual prostitution. There are some places like Amsterdam that have done what they can to clean up the industry, yet even they have struggled. And somewhere like America, the world of prostitution is one of the clearest examples of predators taking advantage of prey. Yet again, libertarians operate on assumptions that do not jive with reality. In this case, that all humans are capable of protecting themselves. This is simply not true, and many of the women who "voluntarily" sell their bodies are usually under the predatory influence of a sociopathic male. Again, it's a bit difficult to frame this within the context of rights and morals because you have not yet defined what you consider a right. If anything you just confused me more.
Oh, and they are also usually hopelessly addicted to drugs, another inconvenient reality for the legalization movement.
This is either moral relativism or you're intentionally dodging the question, which means you aren't at all interested in the philosophical discussion. When someone talks about stealing a car, do you feel it is reasonable to assume they are referring to someone who desperately needed the car for a moral use? If you tell me that you are honestly posing that as a rational response, I will believe you, but I will have to be much more meticulous in explaining arguments that normal people do not usually require clarifications on.
As for the war hypothetical, was that also confusing? Did you not understand the concept of killing someone as an act of war in accordance with societally accepted rules of warfare? Again, I just need to know how pedantic you require me to be in order to have this philosophical discussion.
Not going to lie, considering this:
It really doesn't seem like you are engaging in good faith.