I am. Without delving too much into the religious aspects of it, there are faults to this logic.
I have a problem with your use of the word "prejudice" in that case. It is not a description of the quality of the answer given; it concerns entirely the process used. The "pre" conveys the idea that judgement is provided
before thinking things through.
Even though I disagree deeply with many religious people on the morality of homosexuality, it should be clear that I have virtually nothing to say on the subject. It is true that someone people will fit what is likely a caricature of religiosity, namely that it is an exercise in trained gullibility, that they just say it's bad because the book says it is bad. Those people I would call bigots because it is truly is the case that they dug their heels in the ground without bothering to even ask what others might think about it. In that case, it is truly a prejudice: they respond to things they poorly understand, taking positions against people they do not know and without the need to check in with people who hold opposing views. On the other hand, there are also people who reference the Bible at least in part because they believe the stories it contains can illuminate human experience for everyone, including people who do not hold the authorship to be divine. These people can expand for hours on a handful of lines, relate them to events they lived or to events other people live. They can raise questions, ponder opinions that people such as ourselves (who think homosexuality is a perfectly legitimate way to live your sexuality) hold and might even have debated the issue with homosexuals, sometimes even homosexuals they consider to be friends or even family.
If I apply the definition of prejudice properly, I am more of a bigot than they are because I know far less, have though far less about it, before taking a position. The only salient difference is that I provide a secular argument and that my judgment comes down on the side of homosexuals -- clearly, neither of these things is ground for defining prejudice, unless prejudice has come to mean "not leftwing" in which case a large swath of the left today must be considered at least uncharitable, if not entirely dishonest and outright bigoted (in the proper sense of the word). Again, I ask: why I am not bigotted for being accepting for homosexuals on clearly poorly justified grounds while Denis Prager and Ben Shapiro must be bigots in spite of the fact they have worked a lot more than me and many others to explore this issue?
Conservatives will be quick to point out the "not leftwing" as the determining aspect -- that we make a dishonest use of words to attack conservatives instead of attacking their ideas. The game I am trying to ask you to play is whether you could make a plausible argument to reply to my question that could potentially satisfy at least some conservatives you're not just being blinded by your politics. I think it is a serious problem because it gives some people an excuse to overlook your arguments. They can just label it a leftwing diatribe. Clearly, some religious conservatives
are bigots, but not all religious conservatives can be said to be bigots and until you draw that line somewhere else than the impossible "just become a social liberal," you will deny yourself the capacity to influence millions of people who might change their mind, find new reasons to push for similar policy, or soften their opinions because that friend who is a liberal of theirs isn't so unfair to conservatives.
If you're as tolerant you claim, find a way to draw a bigger circle.
The most compelling, I think, is the idea that "because it has survived so long" gives it gravitas. Slavery existed for millennia. There are some that still believe that it should be given deference because of this.
It was possibly the weakest claim I have made and I will readily concede it is too naively stated and too simplistic as it stands to be a good argument. Many bad things do survive, as you pointed correctly.
I am a confirmed heterosexual. That condition does not prevent me from being tolerant of homosexuality, bisexuality or anything else. Not being black does not prevent me from being sympathetic to the conditions that are suffered by that population simply as a result of birth with higher concentrations of melanin.
On that much, we can agree, as far as we all understand tolerance says something about what you do not do. Tolerating homosexuality isn't a great feat of morality. It just means "live and let live."
