You're right; you are perfectly free to form your own opinions AND express them. That's a great thing about freedom. But as many replies show, expect people to reject your opinions and possibly insult you for them. They're free in that form of opinions and expression, too. I also agree that the government, courts, laws, and police should keep out of peoples' private matters especially when it's fully consensual for all involved and causes no harm to those involved (note this would not apply for actual animal abuse such as non-consensual sex and/or anything that result in injury and harm to the animal).

Contrary to what people almost always say regarding sex with animals, animals are fully capable of forming feelings of consent/acceptance for sex or lack of consent for sex or rejection of a particular partner, and they are fully capable of communicating that through nonverbal means such as vocalizations and body language. However, that's for higher order animals; lower order animals with smaller brains live and mate more by instinct and stimulus-response. An octopus may be intelligent but I really don't know what capacity their brain may have for actively choosing a mate, actively choosing whether to accept or reject sexual advances, and for communicating that consent or rejection.

As far as legality goes, I'd like to see laws keep out of it because I want to see Darwin in action when a human tries to have sex with an octopus. The options are the mouth, which has a sharp beak like a bird and would probably bite the eel in half, the opening to the mantle cavity where the male octopus inserts his reproductive tentacle (and where the octopus also takes in water for breathing), and the funnel which is the exit for breathed water, jets of water for locomotion, anti-predatory ink, and anal excretions. I don't know what a male octopus would do if a human tried pleasuring his reproductive tentacle. Many species of octopus are poisonous (one is deadly to humans), so with a beak and poisonous arm suckers an overly horny human would be messed up pretty good. I'd have no pity for a human suffering the consequences of unwanted sex pushed on an octopus or any other animal.

If, somehow, it was consensual and mutually pleasurable--I don't know whether or not an octopus (male, female, or both) experiences pleasure from sexual mating--I still wouldn't support the action because from what I read, males die not long after mating and females die shortly after their eggs hatch (although a human couldn't fertilize octopus eggs and would not result in any hatching). Since the sex could potentially result in their (octopus') earlier death, I couldn't condone a human attempting to have sex with an octopus. If the human was injured or died as a result of it, well, they're the idiot who tried to screw an octopus.