An interesting topic, indeed.
Yes, if members of the faculty feel comfortable in posting their political ideology on their doors then it would take an exceptionally confident (and risk adversed) freshman to stand up an utter an option in direct opposition.
OP - is it that you want your student to feel comfortable voicing an opinion and engaging in discussions regardless of their alignment with the general group culture? Or is it you wish to have your student be in a generally like minded community?
Both of my kiddies went to rather a-political colleges. That said, certain departments are going to be, by definition, political. You can be guaranteed that woman/ethnic/gender studies departments are going to have a very predictable leaning. Both kids found it best to just get thru those courses with as little conflict as possible. Their opinions were not ‘of the body’. In the case of DS he decided early on that those who shouted over him when he attempted to present a different position had absolutely no intention of listening with an open mind. It wasn’t worth the effort. He also found that most profs weren’t interested in the opinion of someone in S demographic. Sadly, he just spouted - in excellent written fashion - what the prof wanted to hear. It was not worth the effort/ risk to do otherwise. Since it was the quarter system he took the attitude of “I can suck up to just about anyone for 10 weeks if it will keep my GPA where I need it to be”.
Luckily he was an engineering major. And in that department either the circuit/program/widget worked or it didn’t. No one cared whether or not your were Red or Blue, just that you carried your load on a team and that the bridge you built in the future would fall down.
That said, both kids went to geographically beautiful campuses. Both campuses always rate in the top of the ‘who has the happiest student body’ surveys. So, if things got a bit wonky on campus one could always surf, horseback ride, bike ride, have a beach bonfire or just sit out by one of the many pools. And most of those activities and escapes were available 50 weeks out of the year.
The surrounding town will also affect the general atmosphere. The town where D attended had an occupy wall street presence. It was staffed by about 2 people at a time. They sat under the canopy until dark and then headed to the brew pub across the street. Pretty much no-one paid them much heed. The town liked the students and the students were for the most part respectful of the residents. This is not the case in my home town. sigh.
One of the most open and intellectually free environments my kids encountered in their entire schooling life was in Catholic high schools. (Oh I can just feel the eye rolling). Especially if the Jesuits were involved. They are great supporters of social justice and great supporters of learning and exchanging ideas. The discussions had in some of the religion/social studies/history classes would have cause fits in an public environment. One particular history prof had a very different world view than did my son. They would exchange emails with thoughts and links to data and other articles on the evenings when the class discussion had been particularly lively. At the graduation ceremony this particular teacher pulled my son in for a hug and said ‘no way you get out of this with just a hand shake’.
These schools are proof that you can agree, disagree and agree to disagree yet still have a learning environment where one was not ostracized for being outside of group think.
Good luck in your search