"Being able to hire H1Bs helps hiring managers" for sure, but H1B need to be sponsored by the firm they're working for, with the implied threat of losing their residency right if they can't keep that job. It's blatantly exploitative and not a free market at all, so the "lump of labor argument" doesn't apply in this case. Basically, any support for the H1-B program in its current form means you're supporting a race to the bottom in workers' rights.