Your comparison is flawed at many levels mate. The rigidity of the caste system should itself serve as an indicator that castes were not allowed to venture outside their professed social duties. Brahmins served only as the keepers of liturgical Hindu knowledge, and kshatriyas never needed any sort of sanction from Brahmins for their actions. Where there was political gain to be had, kshatriyas made war or peace accordingly. A Brahmin is not required to sermonize, but just to advice. The silliest mistake that one could make is to think that Imams/Maulanas in Islam are equivalent to Brahmins in Hinduism.
Hindutva can never take genocidal overtones, simply because it considers all those who reside in India as Hindus....Muslims and Christians included. Other religious groupings are viewed as people who've forgotten their Hindu identity, and the effort is to help them remember and reconnect to their roots, not eliminating them. This has nothing to do with which God to worship or what lines to parrot to appease the God, but about fitting in culturally into the Indian landscape.
Obviously, there are grey areas involved in such ideological stances, and they rightfully need to be addressed. But to compare organizations like RSS in their present avatar with the likes of ISIS would be beyond foolish.