You have no clue what people have went through. Whether it's surgery, tragedy, self-harm, or even just little accident's. You have no right to point out their scars and question them about it especially if you don't even know them. It's not just scars either. Weight, height, hair, teeth, body types, etc. People who bring those things up don't know how upsetting it is to know people notice the things you're trying so hard to hide or overcome.
Whenever I was at work, I had two people bring up my scars on my face. I instantly felt so embarrassed and I felt like everyone was staring right at them during that exact moment.
I completely froze and just stared at those two adults that had the courage to ask me "what's wrong with your face". How do people do that? I'm sure they didn't do it to intentionally upset me, but that's not the point.
My point is, it still hurt. It hurts the people you make small remarks about or whisper about when they walk by. They hear those whispers and whether they're about them or not still hurts them and makes them paranoid. People need to stop judging and reminding people of their flaws.
I promise you, they are fully aware they are there. They have to live with them.
Instead of commenting on their physical appearance and what is "wrong" with them, maybe people need to focus on actually making a positive connection with that person because they might need it. You don't know what demons they are battling that involve those flaws or their personal life. Society has made everyone think people should be perfect and flawless and if they have even one thing "wrong" with them that they aren't good anymore. They are still human beings and they are still beautiful. Treat them that way.
Whether you intentionally mean to hurt them or not, it still hurts. If they can't fix it within 15 seconds, it's not worth bringing up.