I've always tried to avoid being sectarian, but I know that it's impossible. What I've discovered though, is that the ways in which I write people off for their beliefs are not based on who they follow, but what they do.
I frequently work with people from all over the spectrum of "the movement". From individualists and market anarchists to old school Leninists, the groups that I'm involved with, particularly SDS and the IWW, invite anyone who can work with us. We discourage the old sectarianism, where one cannot even consider someone else's beliefs as valid. In SDS, people often talk of "assuming good faith," that even if you think that those Maoists/anti-organizationalists/whatever have stupid politics, you should assume that they are here because they actually care about the group. Obviously, there are exceptions to this guideline, particularly old sectarian groups who seek to either co-opt something new or destroy it. But the vast majority of participants in these activist groups sincerely care more about the world and the organization than they do about getting their way all the time.
The new sectarianism, the good sectarianism, is one based on method rather than ideology. It divides up those who empower and those who control. Those who build democracy and autonomy and those who create hierarchies and party bosses. I encourage more people to practice this type of sectarianism, or more properly, methodism.
This may not sound like something new, but I think its important to distinguish between the two types of discrimination. The old sectarianism inevitably leads to tiny groups who fight each other more than the bosses. See the Sparts for proof.
However, the new sectarianism leads us to divide up the organizations which will do our movement well, even if our lines may differ, from those who will destroy it, even unintentionally.
For this reason, I may grumble when working with a Trot who talks slavishly of the "centralized economy" or roll my eyes when some crusty anarchist prattles on about veganism, but I will not for a moment let politics interfere with liberation. Likewise, if somebody warms me up a tale of "autonomous working class struggle," then goes back to secretly report minutes of our conversation to the central committee that puts them in a box somewhere (I'm looking at you here, Freedom Road) I will dismiss them as reactionary.
We must not be afraid to make decisions about what is the direction that our movement should move in. But we must be conscious that the decisions we make reflect what is best for the path of revolution, about which we may not know all the answers, impossible as it might seem to us at the time.