My best guess is that it’s more or less impossible to open the door in flight. The way the mechanisms line up, someone would have to overpower the pressure differential on the door’s surface area between the cabin air pressure and the pressure outside, which is far more force than anyone can realistically generate on their own (unless this man happens to be the Hulk, in which case we have bigger problems and duct tape wouldn’t solve them). So technically, yeah, I guess it’s overreacting because it won’t do anything, a bit like how you don’t punch out a kid for attacking you with a rubber knife because they can’t actually hurt you despite the obviously violent intent.

However, this bit is -not- by any means universally known to passengers, so panic would be understandable. Additionally, while opening the door is not feasible, damaging it might well be possible depending on what he has on his person, especially as TSA is famously unreliable at catching everything, and sufficient damage -could- cause problems with the door -or- compromise the seal and cause a loss of cabin pressure, which would definitely be hazardous for all on board.

As for the man doing it, none of the motives are great. Either he’s suicidal and totally okay with killing hundreds on board with his intended method (never mind he won’t succeed), he’s severely mentally ill to the point of a danger to himself or others, he’s irrationally angry and wanting to destroy something, or he’s a wannabe terrorist. All four of those are valid reasons to restrain someone while trapped in a tube miles in the sky.

No rational, stable person tries to force open a plane door in flight. The very act of trying is suspect on its own.