The legal status of bestiality varies depending on the country. It is legal in Argentina, Brazil, Colombia, Mexico, Cambodia, Thailand, Japan, Russia, Finland,
Denmark, Hungary, Turkey, Canada and Romania, and illegal in most other countries. Lack of laws against it is largely presumed to be due to it being uncommon, or a taboo subject most of society prefers to not think about.
Many of these countries previously criminalized it as sodomy in ancient régime law codes (including being burned in the fire of Portuguese Inquisition in Brazil), but it was taken down once the Napoleonic Code took place without mention to such punishments for sex acts "against the order of nature", with anti-bestiality laws – now punishing its practitioners as sex offenders rather than sodomites – being gradually readopted as society took awareness of the practice as a form of animal abuse.
Zoophilia is the name given to sexual and/or romantic attraction to non-anthropomorphic animals, or to both anthropomorphic and non-anthropomorphic animals. (The attraction to idealized anthropomorphic animals is these days increasingly understood as furry fetishism, and the majority of furry fetishists are no more interested in real animals than anyone else.)
Come here doggie woggie...
Bestiality is generally considered inappropriate, since most people will argue that an animal cannot give informed consent to the act, and therefore that the act marks the human involved as a sexual predator. If, however, the "animal" in question is an adult human in a dress-up outfit, while people won't necessarily understand, they also won't prosecute.
Pro-bestiality groups often make arguments related to other things which people do to animals without their consent, such as killing them and then consuming their remains, or artificially inseminating them, which could be interpenetrated as an example of the "two wrongs make a right" mentality. However, the argument is more often used by pro-bestiality groups to highlight the hypocrisy of the common opinion on animals and that the typical opinions on the treatment of animals needs to be reevaluated.
Arguments in defense of
Defenders of bestiality will specifically split the activities into three distinct and frank categories: fucking, being fucked, and watching people doing the former two (aka zoophile-philia). In the former, consent of the animal cannot be verified, although some may react enthusiastically or nonchalantly to the act, as opposed to attempting to get away or bite your nuts off. However, in the second, it is claimed the animal is completely consenting, as you can't really force a dog to get it up and "give it some" if it'd rather chew a ball, run off or lick its own nuts in preference. In fact, most practitioners of the latter actually claim it's the animal doing the initiating most of the time, and claim that this is how they were "turned on to" the idea of zoophilia in the first place.  It is presumably sheer coincidence that they only perform these acts on domesticated animals and never attempt to convince a wild one to come hither. While it's hard to fault this logic and undisputed that practitioners can love their animals, there is no legal distinction between the two acts.
As for the third, it can be quite easily assumed that if an animal doesn't mind peeing/pooing in public, or care less whether it has sex in front of two people or twenty people or two hundred, it really won't have much of an opinion on whether or not you share porn of it on the internet. Then again, it's not likely to even know either.
Performing penetrative sex on an animal may injure the animal, and it may not be able to adequately communicate that it is in pain or that it requires medical attention.
Even if the sex is non-penetrative or if the animal is doing the penetrating, there is no scientific evidence that animals are able to offer informed consent under any circumstances. Quite apart from the difficulty of communicating such a thing, there is a long tradition of humans manipulating animal behaviour to their own benefit. Even between partners capable of offering consent, such manipulations would count as rape. The inherent power imbalance would make the act unethical even if all other consideration were somehow addressed.
Sex with animals may result in serious injury, as an animal is not cognizant of the limits of the human body. This culminated in a fatality in the 2005 Enumclaw horse sex case (see below). Infectious diseases may also spread from the animal to the human in the process, and good luck getting an animal to wear a condom. Additionally, if you are allergic, it can kill you. 
In the media
In the 2005 Enumclaw horse sex case, Kenneth Pinyan had sex with a horse and died after his colon was ruptured as a result. This incident became the basis for Robinson Devor's 2007 documentary film Zoo. He videotaped the incident, and the video found its way online on various shock sites.
Bestiality was erroneously linked to homosexuality by former Supreme Court Justice Antonin Scalia in his dissent to Lawrence v. Texas, where (in an effort to show that homosexuality should be legislated against) he made the slippery slope argument that if homosexuality (specifically, sodomy) is allowed, bestiality will be next. He failed to note that bestiality was effectively legal in Texas at the time he wrote his dissent. Incredibly, bestiality is still not illegal in several states of the USA, with others having only passed laws against it in recent years.
- Of course humans are animals but the term refers to sex with non-human animals.
- Denmark banned bestiality in 2015 in an alleged bid against sex tourism (), despite the Council on Animal Ethics issuing a statement that there was no animal welfare grounds for the ban – but who cares about such niggling points when politicians, incl. the Minister responsible, have whipped up a moral panic?
- Bizarre Magazine - Animal Sex
- Wikipedia: Zoo (film)
- Map of the Day: Bestiality-Friendly States, Mother Jones, Mac McLelland. May 19, 2010
- "Alaska and Florida consider bans on bestiality", Yahoo News, 21st March 2009.