I was thinking about this quote when I was gloriously power washing my mudhole this morning.
I truly think that anybody that isn't on board with a bidet is because they really have no idea how it functions. I think a lot of people think it shoots water out of the bottom of the bowl after you poop in the water....basically the "dirty water" comment. Or they think it shoots out a wide stream of water, like out of a hose, that soaks your whole a$$.
Find a video online of a bidet that you're interested in buying and show it to your wife. Point out the location of the sprayer and the size of the stream, and the manual on/off so she's not forced to use it. And how much money you'll save on toilet paper.
Also it's about a 15 minute install (and faster uninstall)...if she truly hates it after trying it then just remove it. She won't hate it though.
If you STILL can't get the green light from your wife after this, then you need to re-evaluate the power roles a bit. If I was you, I'd just get one without asking her, install it and just actually show her how it works in person. Tell her she doesn't have to use it if she doesn't want to, but it's something you really want so thanks for respecting that (and respecting your butthole).