If you're transitioning from being a dietary vegan* to a full vegan, I'm aware this may only be the second post here that interests you. So I'll take the chance to say kudos for making that step.
Now, your wardrobe is harder to overhaul than the kitchen or the bathroom. You buy clothes to be at least semi-permanent. I'm not saying anyone needs to bin** the non-vegan parts of their wardrobe right away, although you may prefer to, especially if you can afford to replace the more vital bits. However, if you're being publicly vegan (whether standing behind an animal rights stall or eating a different lunch from your colleagues) then be prepared to explain (to vegans or non-vegans - the former will probably accept that you're a newbie, the latter may take more effort) why you're doing so while wearing leather shoes or a wool jumper. (Fur and silk are less excusable, unless you live in the Arctic these are luxury items rather than staples)
So here goes:
Why fur sucks
-Duh, it's a dead animal's skin
-Animals are generally killed purely for their fur
-Wild-caught fur comes from animals caught in a variety of inhumane traps and often left for days before being bludgeoned to death.
-Fur farms are factory farms, and the normal method of killing is anal electrocution. Niiice...
The good news - the high street is full of decent fakes, if you like that sort of thing. (Check the label carefully though) Other fabrics, such as polar fleece, are just as efficient at keeping you warm.
Why leather sucks
-It's a dead animal's skin
-The leather industry is linked to the meat industry, but is big business in it's own right - even if being a 'by-product' made it ok, that happens not to be true
-Much of the cheaper leather available comes from India, cows are herded long distances to the few provinces where it is legal to slaughter them and treated horribly in the process, and the provinces that allow the killing of cows don't have great animal welfare laws governing this.
-And slaughter in the UK is pretty horrible too, as you may have gathered if you've already quit eating meat.
The good news: leather is pretty easy to replace - non-leather shoes tend to be cheaper.
Why wool sucks
-A fair bit of it comes from dead sheep after slaughter
-Merino sheep are bred to have wrinkled skin and thick wool, meaning that they get skin problems especially in extreme heat
-The wool industry is tied in with the meat industry - yes, sometimes you'll come across a family who occasionally shear their 'pet' sheep who live as part of the family the rest of the time and never get overbred or slaughtered. These are more common than unicorns but I'd venture that they are rarer than otters.
-And also there's that pesky animal use issue - think about your reasons for going vegan, and consider whether it's ever ok for animals to be used for human ends. If we're after full liberation, then why perpetuate this form of use?
The good news - there are plenty of other fabrics out there to wear and to knit with. Come and look at my a) winter wardrobe and b) yarn stash for evidence.
Why silk sucks
-Silkworms get boiled to death for their coccoons
-For a product that is basically a luxury
-Need I go on?
*Veganish, strict vegetarian, vegitan/vegetan (sounds like fake leather imo), insert preferred phrase here - but don't start tearing each other's hair out over who is more vegan!
**Or give to charity, or bury in the garden, depending on your views on it staying in use...