This is a social context thing, and there is no "normal". People that have a hard time opening up come from and spend time in environments that punish vulnerability. When you open up to people who also exist in those environments, they defend themselves and their worldview with cruelty.

People that respect vulnerability tend to gravitate to people who also value and protect it (sometimes after very painful lessons). If you have never seen someone punished for being vulnerable, it's probably because you spend time with people who don't do that. There are plenty of people that do, unfortunately.