Carbon frame in winter

Winter bike, cheap Ribble or Kinesis. Ride it until it self-destructs, buy new one. You'd get 20 years worth of frames for the price of a ti frame and they'd be new every few years.

Rain, salt, dirt, and grit will all destroy the finish of your carbon frame in much the same way they would a metal one. So it depends on what you can aford to replace. No reason not to...

Honestly it sounds like you're trying to justify a carbon frame to yourself (nothing wrong with that). It's just that it might be better to re-approach/reword the question:

-"I want a carbon bike for winter duties, what would people recommend?"