Re: why academia has opinionated...
If you're talking at university level, most Profs actually receive tenures based on the amount of funding they can secure. That is based on the extent of their research and this works out well for people (I am not profiling) who are generally introverted. They may not be highly opinionated or arrogant, but may appear that way...
Obviously, many times they actually are as you describe them since perhaps that kind of attitude is what you would want in a researcher to have when he/she presents his/her findings and is able to make a point...
In essence, what I am trying to say is that at least at University level, the ability to teach comes in secondary from what I understand... That said, there are many people who are exceptional mentors as well as researchers, and may even be very openminded as to hearing out what the other person has to say, but they may not form the majority of the faculty.
Again, it is just my opinion.