I think it's better to drop a single item than to be forced to drop your entire backpack (your entire inventory).
Of course, but it is not the case.
You are foced to drop some items only if you want to move again, it is your decision, not automatic decission.
@Others: Also, you should be only permitted from moving, as this doesn't count for all actions. What you do if you can't carry anymore, is indeed droping a bag or something, to be able to fight freely, but you don't leave it just like that, you stay near it and smash anybody who would try to take it

Taking such item from someone in such state is the same as thievery, what we don't have in PS and it is not sure if we will ever be able to rob a player. As in PS we have unnormal rules about items ownership, we can't base on our reality as much we would want.
How do I act when i enter a tavern, order a beer and relax. I put my helmet off. But where do i put it? I RP that i put on on the table, when in fact it is in my inventory, along PS system mechanics. I can't just put it on the table, because while i still should own it, someone may take it instead.
There was once wish for watching feature, so that you put some item on the ground, but it can't be taken just like that, without you agreeing on this.