I do object when those who disagree with me politically smear my side, or even anyone on their side who doesn't agree with them enthusiastically enough, as racist, sexist, bigot, homophobe, ignorant, redneck, while they claim to be the most intelligent people in the world and the sole source of compassion and tolerance.
I'm happy to have a reasonable discussion with anyone who has at least put some thought into their position and doesn't devolve to slinging insults around when they see facts they don't like.
The two party system coerces us into false dichotomies far too often.
Heck, Fox News itself is over 20 years old. So I'm not sure what "long time" you are referring to.
That is: Yes, there are center-right or right-wing press organizations. Despite that, it is still true that the bulk of the "mainstream" press is no longer center - they have become biased, and sometimes even actively helping Democratic campaigns. That's not what "mainstream" used to be.
Maybe something has happened of late (would love to see data, aside from cable news which I think has obtained strong bias of late). But personally, I believe that if there is a problem, it is more the consolidation of media outlets into very large corporations.
This is a lack of diversity problem, not a bias problem. If "mainstream media" is defined by Big Corporations, you have to include Fox News (News Corporation) and AM talk radio (largely Clear Channel) with the liberal side of MSNBC (Comcast), Time Warner (CNN), Disney (ABC), and CBS. I can easily buy that the fact we have much fewer voices than we used to driving the narrative might lead more to monolithic opinions and groupthink.
Incidentally, I personally find the charges you are making about media actively helping campaigns a bit weird as well, given Steve Bannon's role in the Trump campaign.
"Mainstream" used to be NBC, CBS, and ABC, plus AP and UPI. Of those, UPI's gone; NBC, CBS, and ABC have more-or-less abandoned their role. Fox and CNN are new-ish (at least to a person of my age). So to claim that "the mainstream media" all abandoned the center means "almost all the original ones did" - not counting Fox (or even CNN) in the reckoning. Never the less, CNN and Fox are far more mainstream than Breitbart, which is a marginal fringe player.