Why do humans need to have others share there beliefs.?

Having people agree with your views is a validation of those opinion, it gives you a sense of belonging to a group. The problem is most people want everyone to agree with them and that is impossible. Failure to realize that you will encounter opposition from some people results in an attempt to force their beliefs upon others by using abusive language and at times even physical violence.

To find some kind of common ground. How can you build good, strong relationships with people if you don't know basic things about them, including their beliefs on this or that? Yes, differing beliefs can cause disruption, but if nobody cared enough about anyone to find out even the basics about them then the world would be a sadder place in my opinion. So yeah there are some negative things that come with that, but there is bad and good to everything.

Well your main question and the detailed question I think are asking two different things. Humans need to have other share their beliefs because we humans are a social creature, we like to find others that share similar values as us.

As for forcing our beliefs on others, I got nothing much. I think people just want everyone to see what they see as right.

Because they are afraid that people who are different want to take things away from them, even if that is like usual an irrational belief.

And human beings have weak self-consciusness and weak self-belief, they need always other people to confirm them. (same for confirm to other people, esp women, how beautiful they look and that you still love them)

Wasn't it better you keep your question to yourself? Why the hell did you think you have to "share your opinions" with others?!