Selling graphic cards is indeed a stupid thing to do but selling them in favour of buying new more powerful ones with a little bit of extra money is not stupid at all.
From my point of view, i'm considering to sell all of the GPU's, only so i can buy new coins again. Currently, there is no point of mining when electricity is ~75+ % of the whole income. And again, if i take the money that i pay for electricity, i can buy more coins that i mine..