I'd hate to step into the political mudslinging because there is no end to these argument. But, might as well.

As a statement, it's true that both sides sling mud. Both sides do it. But the right is more successful at it. Also, the right tends to congregate around a few very popular conservative sources, some of whom are known to be very controversial.
The left has MSNBC news. The right has Fox News. Fox is way more successful in the US than MSNBC.
The right has O'Reilly. The left has Keith Oberman. I'm not sure Oberman is even still on (as I don't bother with this "pundit" crap). I'm sure O'Reilly is as strong as ever.
The right has Rush Limbaugh. I'm not sure who the equivalent on the left is. In fact, there probably isn't one since I can't think of it. It's probably something on that one station (Air America?).
Because the right has more popular, controversial figures, it feels like the mainstream (on the right) is responsible. I think that's a personal judgment call. At what point does a fringe person with an opinion (a la Glenn Beck) become mainstream?
Not all controversial statements and not all sources are alike. It's one thing to hear something from a random radio pundit or a biased media group. It's another to hear it from a mainstream news source or an elected Congressperson.
I'm biased and I'm admittedly center-left. To be frank, I feel that people who watch Faux News are really subject to extreme conservative bias. The state of most news networks on TV is pretty sad (MSNBC, CNN included).
I think NPR tends to be one of the best, least-biased news sources out there and it's a shame that those on the right are making it their decision to destroy it.
/rant