I've always been particular about proper grammar, to the point where, if I see a grammatical error in an advertisement, company paperwork, etc, my opinion of the entity in question plummets. I know this is irrational (or at least excessive), but I can't help it. I even get a bit nervous about making a commitment - for instance, signing a contract. It's been a bit of a shock to deal with email communication from my instructors at school and realize that - shock, horror - not everyone cares that much about grammatical detail.
Still, for me, I can't help it. I've made a conscious choice to use "they" as gender-neutral singular, even though this is not technically correct ... and I still feel guilty about it.
In some ways, I'm a bit of a dinosaur. I still "double-tap" at the beginning of a sentence and have no intentions of stopping. I am also even pickier about the proper use of commas, not just for clarity, but for the rhythm and flow of sentences. (So says the musician.) Many publishers seem to be abolishing the comma for anything but clarity. And oh, it sets my teeth on edge, even though I recognize that language is an evolving beast.
That said, it will never be okay to start a sentence with "but" and a comma. That's not how it works!