"It's undefendable" - If it is undefendable, how many other teams are doing it successfully? No one, that I know of....which suggests success is a matter of personnel and skillset.
"It'll cause injuries" - are there any statistics showing that there is a higher chance of injury during the tush push? If there is data to indicate that more injuries happen, then the NFL will take a serious look at a ban. Also, the first time Jalen Hurts fails to walk away from the play even briefly, the Eagles will stop using it. I'm am not advocating this....but I'm a bit surprised other teams haven't found a way to injure the QB while he's under the pile.