Should rabbits be outside in the winter?

What degree is too cold for a rabbit

It depends on where you live, if your rabbits are indoors during the summer, the care you take with your rabbits, the type of predators where you live.

If you have a well equipped rabbit hutch, heated, provide fresh water daily, have no natural predators that can get into your yard (dogs and cats included), and the climate isn't that cold, then it's fine.

I have yet to see a well equipped rabbit hutch, I've never seen one that's heated, I know too many people that neglect to give their outdoor rabbits fresh water, and there are always predators around. Having said that, I'd never keep a domesticated rabbit outdoors, not in winter or summer.