But now you're talking about a completely different issue -- competition from foreign labor pushing wages down. But that's also the same reason why the unions can't really get more money from them. They can't pay US workers more when competitors are able to (and do) pay foreign workers less.

You're also now looking at the company's perspective rather than the employee's. The fact that there are other industries is a benefit to the employee -- if you can go to college and get paid twice as much as a software engineer then some people will take that option (benefiting them), which reduces the labor supply in the original industry (benefiting the remaining people).