Polar bears are grizzly bears that adapted to the expanding ice pack. It's just a cycle. If they all die out and the pack expands, there will be another version of them next time around too.
THAT is what we, civilized mankind, must ensure we don't inhibit by our activities.
I agree with you. Thinking that the polar bears may die out because of something mankind has done is very simplistic. They will either adapt, evolve or become extinct. Just like any other species. Including humans!
"A casual stroll through the lunatic asylum shows that faith does not prove anything." - Friedrich Nietzsche