Everyone telling you to fire half your team has the luxury of never having to look that employee in the eye and telling them you're letting them go because the customer is always right and the employee never is.
Unless your product is so well-built and scalable that it could withstand the next 3 months without any dev support whatsoever, it wouldn't surprise me if firing half your workforce would be tantamount to shutting your doors over this. Plus, it's not like the remaining half will be inspired to work twice as hard, and it's not like "as long as I'm getting paid" devs are beating down the door to replace the ones threatening to leave at half the price. Recruiting talent is really hard, even when you're popular. Most of this board doesn't get or appreciate that.
Here's what I'd do. Unlike that guy who declined to make a wedding cake, I'd say, ok guys, but I make wedding cakes my own way, and I don't customize, so the top piece will be very traditional, and if that doesn't match with your special day, that's not my problem and you're free to take your business elsewhere.
Announce to your employees that you're going to do something similar for the pro-life group. Maybe in the sales calls, say you're going to watermark "right to choose" on printouts or something, and that's an area you won't customize. That oughtta shut up the malcontents and perhaps inspire them to work cheaper for you.
And then when the would-be customer gets all butthurt about your horrible sales skills, no one will care, because you're still willing to provide your service to them, just not the way they want, which is not newsworthy.