Of course, H1Bs can't start companies, so that's not a very good way to look at things - if you don't legally allow category x to do y how many xs are going to do y? A better question is how many could.
But let's just talk about employees. I know I've worked at companies in the past in which the backbone of the work (not all of it, but an important part) was done by H1Bs, and we wouldn't have been able to complete that work and be solvent without the (brilliant) folks that had come over on H1Bs doing it. Those, say, 25 H1B jobs created jobs for hundreds of other folks.
So I'm just wary of thinking that everything is a zero sum game or that immigration is "taking jobs" of "Americans."