So is this a porch or a hallway? As what you have described is the latter in which case it is a completely different kettle of fish
Yeah, he doesn't have a porch. Entering what is clearly the front door and leaving something is to me not acceptable. But then, if it's a plain old front door leave it the hell locked.
I have a porch in my new house, it's an outer door, which I mostly leave unlocked, and an inner door has the same level of security. I leave this locked even when I'm in. Delivery guys if they are in a rush are welcome to leave stuff in the porch and have done many times. They are not welcome to enter my house to leave something when I am or am not here which is why that door is locked.
The place you enter a house normally and leave your stuff isn't a porch. A porch is a secondary entry way that leaves a protected buffer for the normal front door by my definition. By an official definition..
a covered shelter projecting in front of the entrance of a building.
An entrance, foyer, entry hall, mud room, welcome hall, whatever, is what you call the space behind your front door where you would often leave shoes, coats, keys, wallets, phones maybe, anything that you'd want with you next time you leave the house. That is what the OP has and leaving it unlocked is nuts. Burglars can and do randomly try front doors, if they are open have a look and see what small easy stuff they can steal within a arms reach of the door then do a runner.
That stuff belongs inside a locked door.