Is it unsafe to still have iOS 6 running on your iPhone 4S?

I've been observing people using iOS 7 and iOS 8 on their phones and I so much prefer iOS 6 as I do not care so much for the newer features. Many people have been telling me they wish they could downgrade, too. I was told that still running iOS 6 is rather unsafe though by a tech-savvy class mate haha is this true?

No it's safe and actually more useful to you to have the older version. When/ if you upgrade you have to have adequate space, plus it will likely slow down your older phone.
If you're a normal human you also don't like change. If you like the current horse you're riding, run that mother into the ground or till the legs fly off.
Don't follow the crowd. Grow a pair

You can run ios 6, but all apps are now for 7 and later.