Let me break down economics of you a little. Everything works on supply and demand; if it is demanded, it shall be supplied. When you buy a product, it tells the makers you support their processing and creating of the product, and it encourages further production. This is why certain causes (usually animal testers, ect) try to rally people up to not buy a certain product; when people stop buying, demand is lessened, a point is made.
Basically if you buy paper plates you are supporting the idea of cutting down more trees to make paper plates that will replace reusable plates, for the mere fact that you don't want to have to wash them.
That is all.