I'm going to toss in my two cents here, plus a ha'penny for SmellyCat.
I think what Adam is saying agrees with my take. We are all born with various proclivities to various types of sin, that is, we are all subject to various temptations. The temptation is not the sin, the indulgence of that temptation is sin. The difference between homosexuality and, say, drunkeness, is that society still recognizes that drunkeness is harmful and undesirable and we have various programs to prevent, treat, or discourage alcohol abuse and its attendant issues. Somehow, we (as a society) have come to put homosexuality into a special, exempted category all on its own, declaring it a legitimate lifestyle choice. It's just like any other sin, the same rules apply.
Anyway, I treat the purchase of vehicles like the issue of meat offered to idols. I've had three Toyotas, two Oldsmobiles, one Plymouth, and three Fords. Unless the one from whom I purchase the vehicle brings up some moral issue related to the vehicle under consideration, I buy the vehicle on its own merits. I have bought from new car dealers, used car dealers, and private individuals, all with their own moral issues. I don't see my purchase as support for whatever (blessedly unknown) moral issues they may have. It helps that all my vehicles have been used, only once have I bought a brand of vehicle from a dealer that represented that manufacturer, so Ford has never profited from my purchase of a vehicle they manufactured.
I drive a Ford now ('96 F150), but I'd rather have a Toyota. For what repairs have cost me in the last two years, I could have bought a Toyota. Live and learn.
Anyway, to address the original post: I appreciate what you and the boycotters are trying to do and hope I'm not raining on your parade.
My two cents? More like two bits. Got a case of the rambles today.