Re: Confirmation bias is the big one
As Mark Twain pointed out long ago, we all have axes to grind. Given such is the case, the wise/honest thing to do is to recognize one's own biases and try to correct for them. Free and open discussion tends to promote this end, which is why those most wedded to their own ideas or the orthodoxies of their own ingroups will often try to squelch it (unless, of course, they're committed to the concept), or simply withdraw to their own little comfortable groups (caucuses?), so they're not subject to the discomfort of cognitive dissonance. And if partisan or other factional politics start playing a prominent role, it can be very difficult to reach any sort of reasonable consensus (witness what has happened to macroeconomics since the 1980s; or constitutional law since forever).
Another issue is that those most wedded to their ideas are often the very people most motivated to see where they lead. This can actually be a good thing as the necessary research will often be very hard work the "impartial inquirer after Truth" (unless he is particularly dilligent) might well seek to avoid. Would Charles Darwin have chosen evolutionary biology as his field of research if his grandfather had not been an early proponent of the concept? I suspect not. If such people can resist the urge to cheat, or perhaps can be persuaded to collaborate with those much more skeptical so they can "keep each other honest", then they can do very good work indeed.
it is natural for scientific journals and their readers to be much more interested in successes than failures (I don't expect that to ever change), and pride makes it difficult to let go of one's life's work when it reaches a dead end (perhaps this is part of why so many breakthroughs are made by younger researchers); but even experimental failures will often lead to discovery if one is willing to consider the implications (thus, failure can lead to success). A classic example was the "failed" 1887 Michelson–Morley experiment that was a large part of the experimental basis for Einstein's Special Theory of Relativity.