1. There are lots of people who would be better off (using any reasonable definition of better off that you chose) working as an H-1B worker in the US despite all the potential for abuse (real and exaggerated) that the status entails. They'd be better off because the pay would be higher. They might be better off because they like american culture better than that of their home country. They might be better off because their is greater scope for career advancement. They might be better off because they might learn more from their peers in the US. Etc.
2. H-1B workers do have the option of quitting their jobs and going back to their home countries if they decide that the abuse is too much. I understand that this is complicated by the fact that they might have taken out loans, or developed attachments to America. However, I don't think that, on net, this justifies banning them from the US labor market.
Perhaps the strongest claim I'm willing to make is that the vast majority of workers ( >90%? ) currently in H-1B status in the US don't wish that the H-1B option wasn't available to them. And that the vast majority of wannabe H-1B workers would still choose to come to work in the US even after they are made aware of all the abuses.
I'm aware that I'm only comparing H-1B as is to no H-1B at all and that numerous other hypothetical arrangements exist that would be better than both.