Could we all agree about the fact that a criticism needs to be motivated in order to be accepted? I see, in some cases we think that there is no point in engaging with someone, because he or she is not worthy of our attention. But then, it is perhaps better not to engage in criticisms either. (As an easy example: I do not start writing about the wrong opinions concerning India of the owner of a certain coffee shop I know.)
Why do we need to all agree about that? In order to make the few exceptions (be they book reviews or personal attacks) stand out. And, in order to be able to automatic distinguish between fair and unfair criticism.
This, however, makes sense only within the general perspective that we are all part of the same enterprise, trying to make sense of the human heritage, to throw light on problematic issues and to show that seemigly simple one are more complex than one might think (why is the latter one an objective to be aimed at? Because simplicity often means not taking into account all voices, especially non-mainstream ones).
If we are all part of the same enterprise, we will be open to collaborations and dialogue. We will know that we are not perfect, but that each brick can contribute to a common construction.
But what if someone who does not belong, sneaks in? Some may tend to send her away, with reasons which are variations of the fact that she is not worthy/does not have the right approach/does not implement the right methodology, etc. This is all very possible. Still, even in this case, I would suggest giving the newcomer the benefit of doubt and trying to engage in a vāda. If she is open to it, and is ready to offer arguments based on reliable sources, then her new perspective might enrich the common building. I would stop the conversation only when a) the person in question is not willing to discuss and just claims to be right; or b) would like to discuss, but does not want to explain why she is right or gives unreliable or inconsistent explanations for her claims (say: “I am right about X, because I saw it in a dream, but you cannot be right about X although you also had a dream about it”).