When His Holiness the 17th Gyalwai Karmapa met with the Tibetan community in Wisconsin, he warned about the dangers of sectarianism to Buddhism. From the notes from this gathering, it notes:
Sounding a serious note of warning against the effects of jealousy and sectarianism, His Holiness the Karmapa cited scriptural sources that indicate that the teachings of a previous dispensation, that of Buddha Kashyapa, degenerated and were finally lost due to the laziness of his followers. By contrast, the Karmapa said, Buddha Shakyamuni foretold that his teachings would be brought to ruin by disputes among the holders of his teachings.
“Strife between religious lineages is the worst, the most serious form of strife,” he said.
“The lineages of Tibetan Buddhism carry different names based on the lama or monastery transmitting them,” the Karmapa said, “but the actual content that is being transmitted is essentially the same: the realization of emptiness, the cultivation of bodhichitta and the unification of sutra and tantra. When we speak of it, we often make it sound as if there were huge differences, but at heart we are basically all the same.”