Why do we as a society....

💙Mia • Cajun & Proud, Conservative, wife to Royce 4.12.14 ❤️, mother to Bennett 8.12.15 💙
I realize this is CC, where (mostly) anything goes, and I'm not complaining, I'm just genuinely curious and want others opinions. 
I think there is a difference between defending your opinion/belief/choices, and trying to convince/convert/force someone else to agree with you. I am all for standing up for what you believe in, and defending what you are passionate about. But when someone disagrees with you, and their opinion/belief/choices do not affect you or anyone else's life other than their own (or their child's), why do we as society try to convince/convert/force them to agree with us? 
I know personally when I am in a heated discussion/debate with someone about something I am passionate about, I probably get carried away and sound as if I am trying to make the person agree with me, although my intentions are not that. They are usually to try to make the person understand why I feel/believe/choose what I do. So I guess it's possible that is what happens and it just comes off as if they are trying to convince/convert/force the person to agree, but I'd be willing to bet more often than not, that majority of society intends to try and change the persons opinion/beliefs/choices. 
What are your thoughts?