A rule? No, a custom yes, and given your but appeared tpmake it look as if you were making an argument you weren't, I don't see it as pointless that it was picked up. I am just glad to have been of help to clear up your what you meant.
Sorry but you might have noticed that you can’t impose your personal customs on this forum. People just tend to ignore them. You could learn to be more tolerant of people who don’t follow your customs but that’s up to you.
Sure, feel free to pick up on all buts and examine their use and context, if that’s an additional service you provide this forum. My experience on here is that when I say I don’t trust my government in these situations, some posters take that to mean I am supporting the foreign government’s position. The “but” was to make clear that it would be incorrect to infer that I trusted the Russian government based on my mistrust of the British government.
BUT if it seems an unnecessary word and bothers you, just keep flagging that in your usual roundabout, quirky manner rather than immediately and straightforwardly highlighting and querying the “but” in your first response. I’ll just respond to any points that I think actually make sense and help further a discussion.