Leaving your door unlocked, in my opinion, is the very definition of not accepting reality for what it is. It is akin to thinking communism is a good idea, so let’s try it again. The idealized world that many wish for does not void reality. Anyway, leaving your door unlocked, even during daylight hours while you are home, is simply stupid.
The obvious reasons that realists keep their doors locked should be self-explanatory: it prevents those not welcome from simply walking into the home and it also gives warning to the home owner if an intruder is intent on breaching the portal anyway. The commotion of kicking down a door is preferable to the silent entry of a threat. However, there is yet another reason to keep your doors locked at all times that is not as often discussed:
In this day and age of substance abuse, mental ailments, and chronic exhaustion, there has been numerous occurrences of people simply entering the wrong house and getting shot for their negligence. The wide proliferation of cookie-cutter neighborhoods in which every house looks essentially the same does not help. Throw in some intoxication, or even extensive exhaustion after a long shift, and people sometimes walk into the wrong house. Do you want to shoot somebody just because they made a mistake and ended up in your living room where you happen to be sitting in your tighty-whitys watching TV with your Glock 17 next to you? Probably not. You know the best way to avoid this particular negative outcome? Keep your damn doors locked, and have substantial locks on the doors.