I use lol to sound less stern and chastising, it's a common thing in this day and age online, and complaining about it seems really unnecessary especially since you're on an Internet forum where language like this originated.
I don't think that is generally the intent of ending a sentence with lol. It is sometimes, probably, but most of the time it is for trying to convey a light hearted, friendly attitude - like a polite chuckle in real life. Millennials do it a lot.
One day you'll realize that what strangers say and do on the Internet doesn't matter. There are more important things to worry about, and you should look to better yourself before lashing out at others. Namaste, my friend.