That is incorrect thinking. I bet you make a lot of mistakes in life.
First of all, just because the masses participate in something doesn't mean you have to. In fact sometimes it's best not to. Second, you never know who and for what purpose someone is looking at your personal information for. I personally know people who were stalked by people they didn't even know! It is very dangerous to post personal details online. I will agree though that today it is hard to prevent personal details from being posted by others, like information sellers.
My sister showed me social media a long time ago. Why is almost everyone posed smiling on vacation? Why are there no photos of the guy getting kicked out of his house by his wife who caught him cheating? That would be entertaining.
But the really turn off was when I saw one posting that simply said "I just went to the toilet." That was enough for me. I will never join any social media.