If a conservative walked into a liberal convention, they'd be telling me the exact same thing about spreading lies and falsehoods.
What's to say they're not just the lies and falsehoods we buy into?
Name an issue and I'll probably agree with you on it. Historically, liberalism tends to be the "correct" side too (or at least the one we've ultimately chosen). The mentalities on both sides though are, generally speaking, the same. You'll find most people are more concerned about being seen as right than promoting the truth. Politics especially, as it's built to be about being seen as right rather than promoting the truth. Any party or politician that doesn't vehemently promote their position in spite of doubts is one that's doomed to be ineffectual. You just hope you end up right and are vindicated by history rather than demonized by it.
Outside of politicians it still happens, too. Look at any thread recently about various bills. People lambast it based on what they've read in blogs. Have they actually read the bill itself, though? Not likely. Could they be being manipulated and fed lies about things like you claim conservatives are? Certainly. Reality eventually kicks in and rarely are things as bad as the sensationalist blogs and politicians claim. Occasionally it's just as bad as they claim, but far from all the time. This goes for liberal as well as conservative. Neither are immune.
Who's eventually "right?" Usually liberal, at least in my opinion. How they go about it, though? Exactly the same.