This seems like the least of the negative impacts nextdoor encourages. i removed myself after months of watching people on this app become more and more paranoid, feeding off each other. the breaking point was when someonea put out a warning that someone had knocked on their door at 7:00pm, “the wife and i were eating dinner when the rude knock came. we crept over to the window, peeked out, and didn’t recognize the p…
Creeping around and posting paranoid messages is silly but I wouldn't blame anyone for ignoring an unexpected knock. The ratio between people I want to engage with and people I don't is just too low. For every teenage girl needing help there are a hundred proselytizers, salespeople, and scam artists.
On a personal level, an unexpected interaction can lead to meeting friendly people. You may even get some unexpected "reward" out of it: say maybe a neighbor was knocking to see if they could borrow your car, maybe the same neighbor has some plumbing skills and notices the leak in your kitchen, and proposes to fix it for you.
On a societal level, unmediated interaction between strangers is very important for social life and a sense of community. Please note there is a huge difference between unsollicited contact and stalking behavior: a person knocking on your door to ask something is certainly not in the same mindset than someone following you home.
So sure there's scams and salespeople. But if you don't open the door to those, you'll miss plenty of friendly interactions as well. At this point, better not check your email or phone because there might be spam there too?