Even if the sacred cows are all 100% correct, losing is a downside. There's no point in celebrating how correct we are about something while completely failing to act on that knowledge.
More broadly, this seems to be how most of politics (especially recent American politics) operates on either side. Anything is open to debate and discussion as long as it doesn't seriously threaten to make someone change their behavior. You can even persuade someone to change their views, as long as their new views can support the thing they want to keep doing. Humans (myself included) are amazing at rationalizing, and hate serious challenges to their deeply held positions.
But I do think it's a useful pattern to recognize. The best tool I know for genuinely well-intentioned debate is to open with "What would make you change your position on ${issue}?" Unless both people can consciously identify a point or set of points that would be sufficient to alter their belief/behavior, there's not much chance of progress.
So, I gamed this out with myself, because it's a good idea. I had a couple that I can't find serious answers to -
* Gay marriage - you'd need to show me that gay marriage actively destroys society. Show me relics of a village or civilization that went under because it had permissive LGBT rights.
* Abortion - as with LGBT rights, you'd have to show me that a God exists that will send me to hell for supporting the above. I could compromise on certain things, but only to preserve the bulk of it.
I can't figure out a good-faith tipping point for either of these social issues for me (fiscal/geopolitical I can find plenty) - and accordingly I can't really have a well-intentioned debate about it as it would quickly boil down to "yes, we disagree on the sacredness of life/marriage". So, what then?
I wonder how you would feel about partial evidence on those points? Like, if someone could show that societies with permissive LGBT rights are consistently (and causatively) less successful, even if they aren't destroyed? I've certainly never seen such evidence, but I'm not sure where on "no harm" to "destroyed like Rome" my tipping point would be. Or - is the abortion point about non-personhood (maybe not applicable at 8.75 months) or bodily autonomy (applicable right up till birth)?
More generally, though: I think those are just places where you save some time by citing a moral basis. It's like arguing contraception with Catholics - you can skip right past AIDS rates and single parenthood by conceding that they think it's a mortal sin, and without changing that they'll never budge. So if someone wants to talk about traditional marriage or fetal pain or whatever else, you can skip ahead with "seriously, address this one issue or I'm going nowhere".