How do the growers of nuts treat Squirrels?

I have started to wonder how those who grow the nuts that I get to feed the squirrels on my porch treat squirrels. I have also begun to wonder about how growers of other foods that I get treat wild animals. Most of the time when you try to find out from someone who sells nut they will say they cannot give much information about this and they may they buy from a lot of different growers. I could only get information from one grower and the man I talked to said that squirrels are the enemy and he shot and gassed them. I wonder if I have given the squirrels on my deck nut at the expense of the lives of squirrels where the nuts where grown. Is anyone else a concerned about this? If anyone is do they have any Idea how to find someone to by nuts from that does not kill or hurt squirrels? I believe that being told that animals are treated humanely is not enough because they may just be killing squirrels in what is considered a humane way (painless).
I also wonder why sunflower seed are supposed to cause a calcium deficiency when they seem to be a natural food for squirrels. Peanuts are also meant to cause calcium deficiency and I have even read walnuts do. Is this because sunflower seed have been hybrid. I wonder if there is not something missing in our understanding of the causes of calcium deficiency in wild animals.