Conventional wisdom in Alaska is that pepper spray just pisses off brown bears.
We know that bears can take significant punishment and keep on attacking.
Bear Spray proponents claim it stops angry or aggressive bears, but there are very few instances where it is used against angry or aggressive bears, and with those, it has mixed results.
To be fair, shooters can fail to stop bears as well. But bears that are wounded tend to die, and not be a continuing threat. The lives of bears should not be held more valuable than human lives.