I think the problem is that certain views are much stronger indicators of someone being willing to eventually shove their views down your throat. If I was a big corporation shopping for, say, spam filter software, I'd rather sign a 3 year contract with a regular company than, for example, a company that is openly fundamentalist Christians. Why? Because the Christians are much more likely to start randomly making ridiculous changes that only make sense to other Christians, like spam filtering out anything with the word "Allah", etc. They may not do that now, but I need to look further than just right now because I don't want to get locked in to an ecosystem that is going to turn sour. Sure I can always switch, but why not just choose the one that has less risk of that at the onset?

Now some beliefs that I disagree with are less like this than others. For instance if the devs disagreed with me about their favorite movies, I'm not going to take that into consideration, because that's not the sort of thing or the sort of person who is likely to abuse their power to aid that cause. But transphobia? That is exactly the sort of thing that someone, as has been proven many times now, will sit on and downplay until they are given power and influence to act on it. Using their software contributes to their influence, especially in the browser world.

Lastly, all other things equal, I'd rather use the product of a smart team full of smart people, than a dumb team full of dumb people. Transphobia is a dumb belief to have, it is a result of being unintelligent. Many smart people (and let's be honest, especially developers) won't want to work with someone like that. Whether you think that's reasonable or not, it's hard to deny. It's certainly hard to picture any great trans developers wanting to contribute. So a lot of things add up, especially when looking a few links down the causal chain, to make it more than just a matter of whether they believe differently than I do.

unless they start curating things like censoring specific words or searches.

Exactly. How FOSS devs spend their time and money isn't my business, what is my business is foundation financials and whether the software is reliable and safe to use.

I strongly disagree with Lemmy devs on politics and how they run their instances, but that doesn't impact me so whatever.

As long as ladybird devs don't go out of their way to be jerks to trans people, I'm good. The worst I've seen is rejecting pronoun changes in code comments and docs, which isn't a big deal.