The owner of the factory has lots of capital: he owns the building, the machines. Those things are a form of capital, besides raw money. The workers have lots of labour: they are capable of work, and they do all the work. Now who should decide what happens in the factory, how the profits are distributed? If the owner decides, then capital has lots of power. If the workers have a say, then labour has some power. If there is no owner, and/or if the workers decide everything, then labour rules.
@M.A.R. Yes. Unless you advocate true communism.
However, capitalist can be used as short for typically/highly capitalist.
If you have a bunch of elephants, led by Mammutha, the largest of the pack, you could say it makes no sense to call her large, because all the elephants are large.
Or you could say, compared with other relevant entities, i.e. other elephants, she is the largest, so it makes sense to criticise her for being large.
Maybe that didn't make much sense...but I think you already understand what I was trying to say.