This 'Are you sure warning' is not needed, it just controls you to make a second selection.
Who cares if you mark things read by mistake?
Every now and then (on the iPad) this locks up the screen, the only fix is to clear the Chrome browser history!
larryd:
Who cares if you mark things read by mistake?
I do, for one. If I accidentally mark things read I lose track of the Threads to which I might owe a reply.
...R
Robin2:
I do, for one. If I accidentally mark things read I lose track of the Threads to which I might owe a reply....R
I am sure the thread will go to the top of the list again when someone else responds.
Besides, when someone quotes you (turn on notifications) you will be informed.
larryd:
Besides, when someone quotes you (turn on notifications) you will be informed.
I would consider that far worse than a pop-up 
...R
Robin2:
I would consider that far worse than a pop-up...R
Having the small Alert at the top of your screen 'is' very far less worse than a pop-up.
Besides, there is still the issue that something goes wrong (intermittently) with this feature as iPad Chrome screen freezes are only seen when the 'Mark Read' button is tapped.
iPad
That's the problem right there
Bob.
Yes I know, but we have 2 of them, what to do 