Hinduism is not a rigid system, having a well-laid rituals to observe for demonstrating one's conformity to this faith. Hinduism is highly syncretic in nature, that is, it contains the contradictory , mutually inconsistent beliefs.
Syncretic polytheist that we are, it leads us to a few problems.
Firstly, one conforming member may fall into argument with other as to what one must observe and one must forbid to prove allegiance. Any rigid ritual will have the effect of doing to Hinduism just what it is not.
Two, Hindus are highly susceptible to suffer internal confusion and conflicts by putting ourselves to comparisons with new age religions and as a consequence of upholding the differences which we have generated by personal thoughts, one group of Hindus might end up adopting certain rituals as a must, which can bring in a localised rigidity into them.
Thirdly, Indeed the vast level of subdivision within Hindu society is explainable on the factor of our multiple belief system . Hindus were never united; they could never become a strong political and military force. But at the same time they have survived innumerable invaders, and prevailed and survived. Today we stand as the oldest religions still surviving against all forces of change; till date we contain within us almost all the characteristics which the ancient religions have -- polytheism, anthropomorphism, demigod worshipping, spirit worshipping.
Fourth, Hindu societies are highly prone to defilement and impurity. Inspite of our pluralist, multi-belief system the one reason why the impurities do not completely run down into our culture is that we believe in Justice. From the myriad beliefs that we hold, we are constantly in search of the truth, the DHARMA. Dharma is our method of selection of one best thought from our marketplace of beliefs by which each group of Hindus run our community. Hinduism survives despite its multi belief system because of this single biggest characteristic , the Dharma, the constant search of the truth and justice. I think that this characterstic pattern of our polytheism, which underlines how come we still survive, is the best understood explanation why the western theologist describe the Hindu faith as Dharmic religion.