Why do some married people think that marriage is such a safe haven?

I just find it humorous that, being an unwed expectant mother---I get tons of flack and judgments, yet a 2 minute scroll through M&D questions and I am reminded why it's sometimes better to stay single. Do you think some people were naive about marriage? Meaning, they thought just because they got married that they would be secure and safe from heartache? I know there are tons of successful marriage (my parents being one, who've been married for 35 years) but when people get on their "You should have waited to get married before getting pregnant" or "Married women don't have to worry about those things"---do these women "actually" believe that? Or is that something they are conditioned to believe about the safe haven of matrimony?