Everyone has a different perspective. My perspective, is that I was kicked out of the house at 18, stuff thrown on the lawn. Needed a job. Bad. My dads friend dragged me by the ear down to the local prison where he worked, had the warden interview me, and gave me a job on the spot as a corrections officer.
18 years old, supervising 600 hardened criminals on a recreation yard, with the help of about 3 other officers. Yeah, 4 unarmed officers supervising 600 inmates, that have baseball bats, weight lifting bars, etc. You are literally scared to death, but all your training advises that the strong will eat the weak alive, and if you show fear, any fear, they WILL eat you alive. So you have to act and present yourself as an authority figure, with guts of steel, nerves of steel, and scared of nothing and willing to fight and get into the thick of it at the drop of a hat if necessary.
As you can imagine, dealing with that tends to change a person. I have no use for people in general. I dont want them knocking on my door. I dont want them chit chatting with me at the grocery store. And I sure dont wont them approaching me at the gas station and asking me for money. And I pity the fool that attempts to victimize me.
Lots of rambling from me, but basically, this is what Im getting at. We are programmed from little kids to be polite to everyone. Criminals on the other hand, grow up in dangerous neighborhoods. They are NOT taught the same value structure that most "normal" humans. They are taught, and intimately learn, about predator vs prey. They see politeness, helpfulness, and cheerful attitudes as weakness. They WILL use this against you. You do NOT have to be polite to everyone. If your radar is going off that something is wrong, and you think a person might be dangerous or otherwise trying to victimize you, or is otherwise just a scum bag that you'd rather not converse with, you absolutely should not be nice to them. Dont smile at them. Dont be friendly with them. Be direct, look them directly in the eyes, and tell them to back off, stay away, you dont want to talk to them, you dont want to be best buddies, and you are going on your way.
There is a time to be polite, friendly and cheerful. And then there comes a time to be not that. Its hard for most "normal" folks to be "mean" or direct with someone, but its a very valuable skill to learn and "occasionally" practice, in my opinion.
At this point, Im mostly a grumpy middle age man. A product of my environment, no doubt. Do whatever makes you happy. If thats being nice and making new friends, then so be it. If thats walling yourself off and staying away from others, then so be it.