If you're paying H1s less than locals you're violating immigration law. The idea behind the H1 program is to help you when you cannot find local expertise in your specialty and need to recruit globally. It's a very sensitive issue in the USA if you are bringing in less expensive foreigners to "steal" jobs from locals.

That said, it's prone to abuse and I have seen some H1s with really poor compensation due to a weak negotiating position (the difficulty of switching jobs while in-country, sponsored adjustment of status, etc.).