It's wonderful that you have different beliefs than either of your parents and want to hold to those beliefs- that part I got. I'm admittedly not entirely clear on what those beliefs are.

here's the part you are not going to like:
You basically threw in your so's parents' face that you have no respect for their beliefs by going completely against what they believe under their roof while they were hosting you.

Don't be surprised if they completely flip their lids when you try to present it as an adult decision or sharing of spirituality or whatever it actually was. Be prepared for this.

the best way to respond is to acknowledge that you probably could have gone about it another way.

how?
By saving a bit of money, over time, going to an inexpensive motel for a couple nights.
i don't disapprove of what you did, and frankly, who cares if I do?

but ultimately, you really just completely disrespected your hosts and now express frustration with their SEEMING disrespect of their beliefs.

I'm kind of confused how that all works together.

but really, you should apologize and establish boundaries if you want them to respect your beliefs, and the two of you as a legitimate ADULT married couple.
I don't say that to shame you or anything like that, but that [that you have been disrespectful to them] is likely the way they will view it.

I wouldn't blame them either.

ETA: also, pretty much everything that danvb said.

Ha, and you thought I was done!
This:
When you are in another's home, it is not a private setting.