By reducing the holding period you're giving more reason for SP holders to power down and then dump liquid STEEM at a quick price

My point is that reducing steem inflation from 100%-150%( today) to less than 10% is a big incentive to hold liquid steem.

The SP creation rate was the problem, not the holding period.

The purpose of the holding period was to prevent people from dumping the hyperinflated steem. If you reduce drastically the inflation of steem you remove the purpose of the holding period, and so the holding period could be 48h it wouldn't be problematic.