.............. You can't just drop it in a garbage can. If you leave a large box just sitting in the ticket lobby you can expect a visit from the airport police.
Absolutely.
If you abandon a box this size the police with be called. A wide area around the box is likely to be cordoned off while they ascertain the contents, inconveniencing and possibly delaying other passengers.
I was at MSP once when someone forgot a backpack airside and left it sitting in the mall area not far from the F/G SkyClub. A wide area was cleared both airside, where the backpack had been left, and outside in the section of ticketing on the other side of the wall, which was most of the Delta checkin area.