I guess we're always going to need to return to the key issue of 'intent'. I see two aspects to sectarianism - the creation of schisms and the creation of closed self-interested sects.
If a schism is created in order to help others to follow Buddha's path more easily or more successfully then at least it is well-motivated. If the outcome is also positive then so much the better.
If a schism is created in order to punish people and exclude them for being 'wrong', then the motivation is negative. Again, the outcome may still be positive if they then find another successful path.
In terms of protectionism, it is obviously sectarian to prohibit disciples from reading books or attending teachings from outside the sect. It is also sectarian to insist that people from outside are denied entry because of their membership of a different sect.
The worst 'intent' of all is to be divisive for reasons of power and wealth, heedless of harm to others and lacking all compassion.
There are several current situation which are sensitive and upsetting, but this seems always to have been so.
What to do?
Well, I've observed (and carried out) different actions towards sectarianism:
- Work from within to create the changes you see as beneficial to others.
- Work from outside to create changes by various means.
- Criticise adversely but do nothing; except maybe make it it clear how superior you are/your sect is/your guru is.
- Ignore it and focus on your own practice because that is more likely to benefit others.
- Ignore it and work on your practice because you simply don't care and you come first.
The best response IMHO is to examine your own intent and the consequences others may experience as a result of the actions you may take.
If you're anything like me that sequence instead tends quite often to be:
Think I'm right, act, upset people, realise I should have thought it through first, promise myself to do better. Repeat until something or someone presses the 'pause' button and you learn a little compassion and humility. Humble and compassionate people are incapable of sectarianism. We know the path but I know few pure disciples (or even gurus) free from the odd bit of self-cherishing.