Devil's advocate :
Turning on injuries would let J players get called up from time to time and help them see some big league actions a bit sooner. Doing so would also increase the LR activities in both teams.
It would also make spending points in skills that favor a better constitution more important rather than focusing in Offensive or Defensive skills only. It would shake up the meta!
So my counter would be to turn injuries on ONLY in the SHL and not the SMJHL.