Hmm, I think I should clarify my answer. I don't like the idea of fur as a trimming or something where it isn't functional (trimming a hood is semi-functional, I guess). Or something ridiculous like trimming summer clothing. In general, I am against killing animals without a good reason, including for sport (although if it's humane, it's not as big of a deal). But I can't fault using it for a useful function (similar to meat), even if the methods could surely be made more humane (similar to meat).
Fur is warmer than synthetics, to my knowledge, and it is produced from a natural source rather than heavily-processed plastic materials (if you're worried about global warming and all that). It also decays naturally in a landfill, unlike synthetics, and it has a much nicer feel (and arguably, look). It is also probably less likely to be produced by people in horrible living conditions in a factory. Buying it can support the livelihood of native people in a productive way, in some cases. So I think there's a valid argument for using it, even though it's possible to live without it. It's possible to live without many things (like meat) that enrich the lives of many people.