“The Bible has noble poetry in it... and some good morals and a wealth of obscenity, and upwards of a thousand lies.” ― Mark Twain
There's also more to being homosexual than "taking it up the ass." There's commitment, embracing, cuddling, but of course leave it to a phobic to obsess over the one sex act he finds disgusting.
And the two statements NOT equivalent. To be attracted to a specific sex (i. e. biological gender) entails an a priori exclusion of members of the other sex from one's sex life, and that isn't natural; there's scant evidence of any non-human species restricting itself to mating w/members of only one gender or the other. In other words, although there's clear evidence of homo- and heterosexuality in nature, there's no evidence of gay or straight animals.
Furthermore, while certain visible (or tactile) traits may be more prevalent in one gender than another, the large no. of humans on earth practically guarantees that any combination of attributes that one may find attractive are likely to be found in at least one member of both genders, hence eliminating the possibility that one could be either gay or straight, since those classifications imply a total ban on mating w/either a different or same gender.
Why couldn't things be like the good old days when gays had to keep silent for fear of violence and couldn't unite to air their grievances?
Liberté. Égalité. Fraternité.
There's merely homosexual and heterosexual behavior, both of which are natural and healthy, but are the result of an instinctual--but not necessarily genetic--fixation (either masculine or feminine) on a specific set of visible/tactile attributes, NOT a fixation toward a specific gender.
If I found someone whose gender is opposite yours that had all the physical and emotional attributes to which you're attracted, then you'd be attracted to him/her.
To claim otherwise would only mean the criteria in that "if" is not met, i. e. there's at least one attribute missing or that you find distasteful that's causing you to be unattracted to him/her.