'll chime in here with my own observations.
Based on what?
Despite the fact that many people feel that they actually practice "real" ninjutsu, there is no such thing.
Based on what?
The evidence to the contrary far outweighs whatever obscure texts they think legitimizes their "system".
I'm sorry, historical documents from the source don't legitimize the arts, but making up a "system" (frankly completely unimpressive based on your posts about it here) with no basis in anything aside from a tiny amount of grappling competition and a little Army Combatives is?
Commercialism is actually the basis for most of their exclusivity.
No, the fact that Ninjutsu is a historical system is the basis for our "exclusivity" when it comes to use of the term. You cannot "create" a new Ninjutsu system as the circumstances that created it in the first place no longer exist, and if you thing you can do so, you are living in a delusional fantasy world.
I don't object to their belief in their exclusivity, however they remind me of overzealous religionists who proclaim their path as the only true method of salvation.
If that were so, then there wouldn't be so many different groups all taeching the historical systems (Bujinkan, Genbukan, Jinenkan, my schools, Toshindo, etc....). What we all have in common is that we recognise the fact that without a historical link to the authentic systems it simply is not, and cannot be, Ninjutsu in any form whatsoever.
Any historical ninjas need to be taken in the context of tribal and clan societies, and in the overall spirit of human adaptation to their environment.
(Just so you know, you're showing your lack of understanding of simple aspects of the culture you're attempting to defraud again... "Ninja" is both singular and plural, there is no pluralisation in Japanese, so "ninjas" is just wrong.)
No, any historical Ninja grouping needs to be thought of in relation to the social environment that existed in Japan centuries ago, which, so you know, were not "tribal" in any way. As for "the overall spirit of human adaptation....", that's all fine and good, but is in no way exclusive to the Ninja, and in no way makes anyone looking to such things Ninja or practicing any form of Ninjutsu either. Really, these are just empty words from you here, not really meaning anything when you get down to it.
To think that a group of humans engaged in a self preservation method and then standardized and codified it is no great stretch, but to think that their methods cannot be observed and obtained on another path is folly.
Such things can be observed and obtained on other paths, but then they become something completely different. There are many paths like this, but only one of them is Ninjutsu, others get names such as Aikido, BJJ, Karate, Savate, Muay Thai, RBSD, Army Combatives, TKD, and far far far more. But to claim any of these as Ninjutsu does both them and Ninjutsu a huge disservice, the only thing worse is claiming a completely falsified and fantasy-based "system" as one as well.
The concepts and rationales of something are far more important than the titles.
This is nothing to do with "titles", son, it's to do with knowing what you are talking about. The correct classification of things, based on accurate knowledge about them, aids people in communication about such subjects, incorrect classification based on "well, I think this, based on no knowledge whatsoever" is only going to lead to confusion and a lack of weight to anything the one who is using the incorrect classification may say. If you want to discuss Ninjutsu, you have to realise that the only accurate classification refers to the authentic historical systems, and anything else is only going to lead you away from that reality.