Facebook is not a discussion site
I have a facebook account. The nearest I have come to political discussion lately is when a number of people I know put in pro SNP commentary.
If I want intelligent, or otherwise, conversation beyond the level of family and people I went to school/College with, I use Google+.
If you talked about nothing but politics, it could end up even more of an echo chamber than FB though.
I seem to have escaped that by never having intended to talk politics in the first place. My initial discussions included IT in general, Android, photography and travel.
After A while I found that some posters also posted on other subjects and some people from the US were "conservatives" and there were even some from this country who seemed to be supporters of UKIP! Neither of those groups would appear in any echo chamber...
After a while I realised that I was also getting postings from people I didn't know but on subjects I was already commenting on.
There will be different algorithms on FB and G+ but I certainly, regularly, get my opinions challenged. It can be done then.