I have shared my thoughts on mashing in a cooler elsewhere. I acknowledge that my inclination away from it is largely emotional. I don't even like to drink out of plastic cups. I will do it, but it is clearly not my favorite. Whether it is in my head or not I often taste plastic. I think it is an OCD kind of thing: I imagine the plastic leaching ___ into the liquid.
So no, I have no science behind my decision to avoid a cooler MT, but I also don't want one. having said that, I will drink any of Denny's beer! Even out of a plastic cup.