Some people also find cruelty funny. That wouldn't make cruelty funny.
Yes, when talking about people who are Christian nationalists trying to install a theocracy, you may have the words "fascist" and "Christian" in the same article. But it's not in the same ballpark, or even the same sport, as saying you're being called a fascist for saying "Merry Christmas".
If anything, it's motte and bailey disguised as a joke. They're trying to get people to see anyone associating anything even Christian adjacent to fascism as unreasonable people.
But. You can be Christian and not be a fascist. You can go do Christian things, worship Christian gods, attend Christian churches, have Christian holidays. No one is going to say anything about it. The minute you try to force me to accept your Christian things, worship your gods, attend your Churches, and celebrate your holidays over all others, is the minute we start having problems. The minute we begin saying that you are a fascist in addition to being a Christian. Because no one is saying Christianity is fascism. But that's what that "joke" does. It's basically staking the claim that people complaining about Christian fascists are saying that all Christians are fascists. Or at the very least, saying that's a leap you can make. And it's not.
It seems like you don't laugh at the Bee </interpretation>. I don't laugh at SNL. Or Trevor Noah. I cringe. But it's still satirical comedy nonetheless because lots of people do laugh and I would be the first person in line to protect their right to make fun of Trump or Christians or Republicans. Without this right to push the boundary, especially in a way that makes people laugh, then it really does start to look like fascism.
"American Christianity is fascism, all American Christians." https://twitter.com/MayMayGraves/status/1564745487378530305
See also https://twitter.com/PatRyatt/status/1576708937725927424 https://twitter.com/sladeofyaupon/status/1309652727660785664 https://twitter.com/timberwraith/status/1529918154721398784 https://twitter.com/VofDestruction/status/157724863750710476... https://twitter.com/JasonIsCreating/status/15327851529334743...
Also, jokes that are about literal things are, well, usually more boring. Have people called me a fascist for saying Merry Christmas? Nope. But... have I seen legitimate news outlets using the word fascist and Christian in the same article? Yep. Did it indirectly draw a connection between the two? Sure seems like it to me. Hence, the joke.