Why do Liberals ASSUME that if you don’t agree that you are a FOX watcher?

I asked a question on Y/A this last week, (And commented on several articles things that I have read which leaned heavily towards liberal ideals) and immediately got lambasted and told I was a follower of Rush and Fox News. Problem is, they are listening to people who presume everyone watches TV or gets the Rush show on Radio. I have not had TV since 2005 and where I have been living (since 2007) The only RADIO stations I get are PBS (VERY LIBERAL) and Country western! Neither of which I turn on until between 6PM and 8AM when it is Jazz, 70’s music and BBC). The thing is I use my eyes, ears and brain to process my experiences and research THEN I decide what I believe or not, I do not rely on media of ANY kind to decide what I believe in. I would hope those who tell me off for my beliefs would do the same, but it seems that their answers are fabricated by what media is telling them rather than thinking for themselves.