I enjoy a good debate, and am not shy about sharing my views if I feel strongly about them. But I also realize that no matter how thought-out and articulate my arguments are, not everyone is going to be won over. That doesn't stop me from offering them (politely). For instance, if someone says that having the government buy everyone purple bunny rabbits would be bad for the economy, I share my theory that it would be *good* for the economy, and explain why I think this way.
I don't think that Kara's comment to Maria was a slam at you, OP. She was just acknowledging to Maria that yes, they are on the same side of this issue. Kara hasn't done anything IRL to indicate that she doesn't value your friendship because you happen to be on opposite sides of this one issue. In fact, she's been a great friend to you, which is as it should be.
Some of my FB friends have made posts on controversial subjects I don't agree with. I generally ignore them *unless* a debate starts, then I politely speak my piece (see above).
It is possible to have great friends who don't share your views on certain subjects. My HS best friend and I were as close as sisters. We drifted apart and reconnected 20-plus years later. We hadn't been the least bit political in HS, but in the intervening years, I've become a staunch Purple Bunny and she's a staunch Green Unicorn. We're still friends. In fact, when she visited and found herself in a houseful of my Purple Bunny friends, she put her arm around me and whispered, "Don't worry, I'll keep my politics to myself!"