Zipper bags are so handy! I like that I can fit leftovers in them or snacks, carry foods to other places in them, or separate a family pack of meat out into portions to freeze. I also like to coat stuff in them. I make this yummy snack of spiced crackers in a gallon bag, then I store them in it...works out great!
So I have this heavy usage of zipper bags, but I hate throwing them away! Lots of bad going on there: Plastic is made from petroleum and therefore feeds our global demand for petroleum; the time required for plastic to decompose is, oh, wait, plastic DOESN'T decompose (http://www.livescience.com/33085-petroleum-derived-plastic-non-biodegradable.html); plastic is about 80% or more of the waste material gathering in the various trash vortexes in our great oceans; and the beauty of the plastic bags caught in bushes or on fences waving in the wind is lost on me, I don't know about anyone else.
This dilemma is mitigated well through frugality. The best thing to do (for the environment) is to not use them, but lets be a bit more realistic in this day and time. My mom always washed and dried her zipper bags so they could be of use more than once. She got this habit from her mother cleaning the foil from back in her day to use multiple times. I adopted the practice too. When I wash my bags of course I also do that frugally. I'll gather enough of them to make it worth the time and effort, then rinse them all in a container of water before applying the soapy scrubby to the inside and outside. Then 2 rinses and they decorate the kitchen on jars and whatever I can hang them over to drip dry. My family is less than appreciative of this step, but they use the washed bags too.