The argument is very simple. I've refered to it in the past actually.
Throw someone in a cage and ask him how eager he is to get out.
Now throw someone in a cage with the keys and ask him the same question.
The idea that people need to be locked in to hold is stupid, using force to achieve something is never a good solution.
Did the 3 months locking period prevent whales from selling? did it prevent the price to go very low? NO. All it did was slow down the price discovery process and delay transfer from weak to strong hands
Would people buy more bitcoins if they couldn't move them for months? Nope, they would do the exact opposite. People want control over their money, they want to be able to access their fund at all time. If you remove this ability from them you are not going to get any investment from them.
Also I think the market would be healthier with a short lock time period as there would be more liquidity.