I can then assume that masochism, even if the recipient and the giver are in agreement, is immoral?
"Hurt" can mean different things depending on context, NJ, you know that. Clearly, voluntary injury is not considered immoral, or boxing, wrestling, football, etc would all be considered immoral as well. "Hurt" in the context used implies non-consensual harm, and anything else is semantics.
The question of morality concerning homosexuality or anything else depends entirely on one's definition of morality, and that derives from the system of ethics you ascribe to. One who believes that personal acts that don't harm others (just to be clear, I mean non-consensual harm or grievous injury) are ethical is going to have a completely different opinion on the morality of homosexuality than one who believes in the ethical system of "God said so."
We all know this, and I don't honestly believe a person with a literal biblical ethics system will be convinced by the logic of other ethics systems.
In all seriousness though, society views it as immoral behavior. This isn't cultural bias either, as I've heard of no civilization where this practice has been accepted. (Not that the acceptance of something automatically makes it alright).
Whether you've heard of a civilization that condones it or not is irrelevant. Simple rule of majority opinion has never been and never will be an effective method of determining what is moral, or anything else (and before you say it, no, the US is NOT run by simple majority opinion - the three-branch system of government with checks and balances exists for the express purpose of preventing the oppression of minorities by the majority). It's a simply an appeal to popularity.
Truly useful ethics systems for a society that does not oppress varying religious beliefs (or no beliefs) need to operate on something more objective than majority opinion (note that interpretations of ancient texts differ wildly enough to exclude them as an objective source or morality, even leaving aside the fact that to do so forces people who do not ascribe to a particular faith to follow the tenets of that faith). Objective, non-consensual harm is one effective method of determining the morality of an act.
People can do whatever they want in their private life. But it doesn't make it moral because its done so privately. Most murders and rapes are committed privately. But hey, if you want to smear peanut butter all over your boyfriend, while dousing yourself in squirrel urine, have your fill.
Murders and rapes cause objective, non-consensual harm or grievous injury. Squirrel urine and peanut butter do not. Comparing the two is ridiculous, despite the...oddness...of that particular fetish. Since homosexuality causes no objective harm, it cannot be immoral, even if you find the act as odd as "dousing yourself in squirrel urine."
Of course, nobody is born covered in squirrel urine, or born a rapist or murderer, either. People ARE born attracted to the same sex. This means that considering homosexuality to be immoral is on the level of claiming that being black, or asian, or white, or male, etc is immoral. Clearly, states of being that involve no choice cannot be moral or immoral - they simply ARE. The evidence shows that sexuality is such a state of being. Those who believe otherwise are in denial, and I would challenge any of them to explain exactly when and how they decided to be straight.
Every time a fundy breaks the laws of thermodynamics, Schroedinger probably kills his cat.