And why are we downgrading and not pushing 0.8 fork if bug is in 0.7 ?
Because 0.8 can accept the blocks generated by 0.7, 0.7 cannot accept the blocks generated by 0.8.
So on the one hand, enough miners can backpedal to make sure the 0.7 chain wins until we fix the problem, meaning everyone gets to stay on the same page, or we try to lean on the 0.8 block which will leave half or more of the world's miners and nodes on the wrong side of the fork until they all upgrade.