Humorous. First of all, people who have a problem with homosexuality on religious grounds often do not consider themselves 'Homophobes' because this heavily implies mindless derisive behavior. However, the fact of the matter is, it is possible for someone to have a problem with homosexuality on religious grounds and be a homophobe. See: Crusader fanatics.
The thing is though, your entire argument for the thought that beefeater is homophobic is on the grounds that (Assuming he's a Christian) Christianity is crap. You two are at a deadlock. If you want to win a debate, bring someone down with their own logic, not your own. It's unfortunate that many people don't understand this essential rule of debates.
Now, first point. I disagree with one of Beefeater's points as well: Emotionally. This isn't some form of masochism, they actually ENJOY it. It's a matter of free will, as is all sin. I also partially disagree with physically. I have seen no medical evidence that homosexuality causes STDs to be transmitted more easily than heterosexuality. I would, however, consider this a viable point to be used in a debate about the morality of bisexuality. (Way too many 'alities' here, it's starting to sound weird in my mind.)
In response to the second point, while divorce is the absence of a relationship as husband and wife between the two parties, this does not undermine the traditional family model (And I don't mean the 50s-era model.) in the way that homosexuality does. In short, ending a relationship is one thing, providing a socially acceptable alternative to beginning the relationship is another. What would cause more harm, the assassination of one of Edison's parents before he was born via time-travel or the assassination of Edison after he does his life's work? (I know we don't have time travel, it's just a hypothetical example. I'm putting this here because of some ridiculous arguments that I've seen.)
And about the third point cited, that's not exactly the point. The point here is, that people are unwilling to see it as a deviation (In spite of the fact that biology states that it is.) and thus, are unwilling to look for causes as opposed to just leaving at, "It's inherent, we can't help it."
Fourth, I partially agree with Brendan here. You gave him no reason to believe that homosexuality was equivalent with self-harm. However, the way that people celebrate St. Patrick's Day is entirely up to them. (Side note to the 5th quote, not the most effective picture there.) 6th point, Objectivity is one thing, but once a belief is forced upon another, it ceases to be belief and becomes oppression. 7th point, see above. 8th point, "Some of my best friends are <insert group here>" isn't that great of a defense. However, given Beef's apparent lack of experience in debates, I would assume that he's being honest. Furthermore, mockery has no place in a civil debate. (Yes, I know that sounded like I'm wearing a monocle or something.)
9th point, see above, you're using your logic to try to convince him, that'll never work. 10th point, you definitions of 'Special protections and privileges' are obviously different. Brendan views it as something that would give anyone whom engages in homosexual behavior an advantage over those who do not. Beef, apparently views it as same-sex marriage, and similar sanctions. (I'm using second person because I assume both people will be reading this.)
11th Point, Actually, this is relevant, Beefeater. If it were to be proved that it's a matter of genetics, then a good deal of arguments against homosexuality will go out the window. Furthermore, Beef, not the best choice of words. It implies that there is, in fact, harmless homosexual behavior something that I believe we can agree upon the nonresistance of. 12th Point, that retort actually implies that you believe that this is a matter of behavior, and not inherent quality. I'm sorry if I've misinterpreted, but please try to be more clear in the future (Not trying to sound smug.) Furthermore, adultery as a crime does NOT mean that we're going to start executing or mutilating people. Seriously, insults and mockery don't help your case.
I'm going to take a break now, that was long. (I realize that I made an obvious statement.)