Grid use charges currently are based upon your consumption of electricity coming in through the grid. If you use more, the grid charges are figured in automatically. If you use less, you pay less for the grid. This seems very fair. Now, if I reduce my grid electricity consumption for whatever reason, the utility company gets less money for both grid and electricity. I may have improved my insulation. I may have shut off appliances or they are now more efficient. Or I may be generating my own electricity via solar PV. Its none of their business, and I shouldn't have to pay them money just because I use less of their product.
You may be able to make the case that they shouldn't have to buy my excess power. No problem, I'll just size my PV array such that it meets my typical needs and not have any significant excess.