(imo 80% is more than enough to prevent shenanigans -- in most contexts anything even slightly controversial cannot get near 80% support. And in this case, the voting is weighted by stake, and the market value of the Tez would presumably decrease if shenanigans were pulled; Tez-holders would probably be reluctant to do something that is both wrong and also would clearly decrease the value of their holdings. In fact i think the threshold for amendment should be lower than 80%; i might chose 67% if it were up to me)
(imo 80% is more than enough to prevent shenanigans -- in most contexts anything even slightly controversial cannot get near 80% support. And in this case, the voting is weighted by stake, and the market value of the Tez would presumably decrease if shenanigans were pulled; Tez-holders would probably be reluctant to do something that is both wrong and also would clearly decrease the value of their holdings. In fact i think the threshold for amendment should be lower than 80%; i might chose 67% if it were up to me)