If you can implement a simple feature/workflow to prevent accidents, why not?
The feature does nothing to enhance or improve on the current design. The only reason the problem is occurring is because the users are not taking responsibility for their actions.
If they were paying attention they would never have switched the item and this feature would never need to be implemented.
If this gets implemented then it opens doors for other pointless features to be added that remove the player from the game.
Sorry, but once again, item lock is a useful feature. A human can never pay attention for 100% of the time; it has nothing to do with personal responsibility. Currently I check my dps and stats with a cursory scan over my gear because I am paranoid about losing my gear. Yet, there are times (especially after long runs) when I can still accidentally swap out equipped gear. I already have a friend who is even more careful than I am, but still managed to lose his gear on 1 occasion. That tells you it's not about being responsible or what else, but because no one is perfect.
And the thing is, losing gear is permanent. It is irreversible, unlike the examples you have quoted. Picking up items unintentionally, or misclicking on a monster is hardly something catastrophic.
Item lock is not pointless. I had an earlier post about this: "if item lock was implemented, would you use it?" Would you?
I would even go one step further and challenge Blizzard to implement it and run the percentage of players who keep their gear locked on a permanent/semi-permanent basis. You really cannot run away from hard numbers here. That was how the legendary "column of light" was implemented, as opposed to suggestions that were more superfluous (colour changes/pickup radius). Players are already concerned about missing out on legendary items, what more losing pieces of gear they have deemed to be superior enough for them to wear it? Besides, item lock has no bearing on people who choose not to use it.
Suggestions which are good enough will eventually push their way through, because it is a real issue, and people will keep asking for it. Threads on losing items will appear again and again until something is done, and it's not because I'm bumping it. It's because everyday there are new incidents of misvendoring equipped gear. I'm not crying about game difficulty here; I'm asking for a useful feature that will improve gameplay, convenience and safety for everyone. I'm looking forward to that day when I don't have to keep staring at my stats and gear to ensure I did not sell off my gear with each town visit.