(FTR: I am not downvoting you).
I share your sentiment. I used to be active in a local food buyer group (7-15 people getting together to collect vegetables and food from local producers) and I saw how to the tribe factor plays a huge role in one's allegiance and political stance.
Basically, people gather to be together. The end goal was second to that. Buying local or organic food ? No brainer. Joining the Sunday demonstration against the nuclear plant ? No room for debate. It's assumed everyone will go and it'll be friendly (almost in a kid way) and everyone is in it together. It's about the tribe and mutual reassurance (are we all friends ? are we all okay ?)
Scary thing is when you realize some people fall into the happy gang of buying fresh vegetables from the farm and spend an afternoon or two during summers tending to the crops with the farmer (and then have a nice bbq) but some people, because they were put in classroom A or B in elementary school or anything else really, end up roaming the street at night looking for troubles.
It's all really basic physiological needs: humans like to be together. The political (in the city sense) reasons for that often seem to come second.
So, yes, the exterior signs of belonging to a group have to be defended. And the online discourse make it looks like everyone is a hard-liner and conversations get hot real quick.
It's like the vegan thing on Imgur. I know some hard core vegan. None of them are anything like the straw men I see, the made up extremist version of vegans, being derided on the front page.
There's one guy in my facebook friends who can't let two days past without posting something along the lines of "do vegans think of mama carrot when they eat baby carrots ?". I counter joked once that he must have been bitten by a lettuce or his parents forced him to eat his soup too many times when he was a kid to hold such grudges against vegans.
Now on the other hand I have another friend in the first stage of veganism that can't let two days go without posting outrage cryporn about the beef or chicken industry.
So. They all clash. Social networks are social status validators and all the tribes are mixing in but their core values aren't compatible.
Sorry, I am rambling.