I think we can all agree that there are trade-offs involved.

I also think we can all understand that the airlines will do whatever they can to displace risks/costs onto others (see the existence of the TSA) and minimize their already tremendous regulatory burdens (see how they lobby).

The airlines already do a good job of keeping aisles and passenger footwells clear in my experience, and US flagged airlines are extremely safe compared to other forms of transportation. What would the costs be vs. the benefits of locking overhead bins? I don't know.