At the very outset let me state that many theories have been propounded on this earth. Some of them survived for some time and then gradually passed out of existence; others emerged like meteors, exhibiting their dazzling radiance for a very short time, and then vanished into darkness. The mere existence of a theory is not the essential point; what is important is whether the theory promoted the welfare of all, the spiritual well-being of all - otherwise its advent on this earth was quite useless. Such useless theories are not even worth mentioning.
Any theory will contain the seed of well-being if its firm foundation is sama-sama'ja tattva. It may survive for a very long period - even for eternity - if it cherishes the ideal of forever promoting the welfare of all. This is the essential point.
