I'm a vegetarian with leather shoes, if I could get decent shoes that weren't leather I would (are animals killed for leather, or is it mainly a by-product of the meat and dairy industries?)
If my survival depended on killing animals to eat or clothe myself I would, otherwise no.
The most “luxurious” leather is supplied by new-born veal calves and sometimes even unborn calves taken prematurely from their mother’s wombs. So it's not a by-product in these circumstances.
Leather apparently accounts for approximately 10% of the animal’s total value, making it the most valuable part, pound for pound. So it's not a by-product here either.
And if you want shoes that will calm your conscience there are companies out there that do make "Vegetarian footwear"