It could be bad in this sense; If the hybrid offspring are sterile, as most if not all hybrids are, then each hybrid born represents the end of the line for that particular bloodline....as opposed to if the male that sired the hybrid had mated with on of his own type of bear.
I guess it depends on whether the two types, Grizzly and Polar, are close enough genetically that the progeny of a “mixed mating” are still sexually potent and not sterile.
Most hyrbrids are sterile? I don’t think so.
One of the definitions of species is that they can interbreed. Thus, are the polar and brown bear really different species at all, or are they no different than different breeds of dog or races of people. The physical characteristics of human races vary just as much or more, and until recently they were fairly homogenus in their own areas.
Yes a donkey and a horse are going to have sterile offspring, but a Zebra and a shetland pony will produce a fertile hybrid.