This flat claim only makes sense when you consider foreign employees to only participate in the US economy through their employment.

But they are in fact full-fledged human beings living physically in the United States. They are buying groceries, paying rent, getting their haircut.

Once you realize they are fully participating economic actors, it is much less clear whether they are a net positive or negative.

To my knowledge economists do not believe this one is black-and-white, but that's much more of a question about the issuance of H1B visas they begin with anyway.

they also pay into taxes and social security without ever hoping to get that money back

For tech especially I don't think that's necessarily true.