I propose that banks' "current" earnings don't reflect anything but hong kong phooey accounting. Take a look at the US bank earnings for Q1, they were all able to report huge profits after the accounting change permitted them to ignore balance sheet valuation issues. So i ask you in reverse, what makes you think the "current earnings" are real?
Soveriegn wealth funds now announcing sales of UK bank stocks, see Barclays today. Further evidence that it is much easier for a government to give away money, than it is for a government to sell for a profit. Injecting money into banks brings its own downfall, the shares themselves. But don't forget about the 2nd hidden downfall, the continued supply (too many banks) issue when borrowing demand will clearly be low for years.