Earlier quoted context omitted.
You're a) expanding the labor pool with b) people willing to work for less money than the locals. How you think that doesn't drive down wages is beyond me.
You're making a positive proposition in the domain of economics. You're obligated to show evidence of it if you can, or at least propose a mechanism people can debate. It's entirely feasible to do so. But good luck with that; I think the data shows that it's not a very pronounced effect.
Yes, you're right, H1-B visas and offshoring have done wonders for the average US software engineer's wages.