There is. Let's call it the rule of being interesting to other people. Your mother cares how you feel because you feel it, but other people care how you feel because you argued it well.

You're right. You can hold whatever opinion you want, with whatever evidence or lack thereof you'd like. It is a free country.

You'll have a hard time convincing most people that way, thankfully, though I'm sure it does work for convincing some.