From the Mahaparinirvana Sutra we can see that there are three kinds of Buddha-nature: (1) the potential Buddha-nature—not yet realized—which is in all living creatures; (2) the Buddha-nature developed by the right discipline in the analogy of transforming cow’s milk into butter; (3) the final or perfected Buddha-nature resulting from the development of the original potentiality.
Do Buddhists get this wrong? Yes, they certainly do. It seems they are more interested in saying what the Buddha did not say than what he said.
Over the years on various chat rooms like the now defunct E-Sangha I argued from the position of the English translation of the Mahaparinirvana Sutra (tranls. Kosho Yamamoto) almost to no avail except that some people took up the banner and carried on, some of whom I suspect are still battling. As Mark Twain aptly said, “It's easier to fool people than to convince them that they have been fooled.”
To believe that just because all creatures have the Buddha-nature this fact makes one a Buddha, requires that one cross a bridge when there is no bridge yet made. Looking at the other side of this immense chasm is the perfected Buddha-nature. Standing on this side, we only have the potential to become a Buddha. The means is still absent—the bridge is missing, that is, the Buddha-nature developed through right discipline.
Few feel the urge to build that bridge. It seems almost impossible for them. But this is because most people are still enamored with the mundane world even in the face of great misfortune and tragedy. They reason, why give up a sure thing for a dream?
Still, it is almost a cruel deception to teach people that they are already Buddhas; that they don’t have to develop this nature through study and discipline, or maybe that if they just meditate they will eventually grow into this nature.