I'm not sure what "most liberal" means?
Does this mean "most liberal in giving?"
Or does it mean "most liberal (i.e., "loose") in behavior?
I'm sure we're not talking about the political views, are we?
I think Nyingmapas could be viewed as the most "liberal" in giving.....this is because the Dzokchen Tradition, in general, stresses Pointing out the View as a pre-requisite, really, for all practices. Therefore, in many (most?) Dzokchen lineages, which are pretty much all Nyingma, Pointing Out is given first. Rushen, Ngondro, Kyerim and Dzokrim are all understood as practiced from the POV of "View." Even so-called "lower Tantra" classes such as Mahayoga are practiced from the POV of Ati. by contrast, many Sarma schools work through Mahayana practices, through ngondro and Kyerim practices, before really fully presenting the "Highest" explanations....(This is generalization, I know....many of the current Sarma teachers are influenced by the Rimay Movement, which was largely a Nyingma-flavored development).
I also think Nyingmapas are viewed as the most liberal in their behavior, whether this actually the case or not is a separate issue. The very nature and history of these lineages presupposes a "nonmonastic" framework, historically. This is not to say Monasticism is not important to current Nyingmapas--that would be foolish. Also, those familiar with the Samayas of tantric practices would be quick to point out that seeming "liberality" in behavior could be mistaken interpretation on the part of the viewer.
Also, on a tangent, it's not really correct to say that the Jonang Lineage was subsumed by the Gelukpa. It's true that the modern Geluk lineage did incorporate Kalachakra teachings and practices from the Jonangpas, just as they incorporated, for example, Shangpa Kagyu practices, and Sakya Practices, etc., as filtered through their own presentation of tenets, etc. But the philosophical underpinnings of the Jonang lineage, specifically the Shentong of Dolpopa, as presented largely by Taranatha, were repressed, even vilified. Somewhat for political reasons, and somewhat, by some teachers, as seemingly anathema to Tsong Khapa's views. but there were, and are, small enclaves of people maintaining the Jonang practices, and they have recently resurfaced. In recent times, Kyabje Kalu Rinpoche, and his disciple Kyabje Bokar Rinpoche, have sought to practice and propagate this lineage and tradition of Kalachakra.
Shentong is not "one thing," either, but has been interpreted in a number of different ways. As I understand it (not very well), the primary exponent in our times, Khenpo Tsultrim Gyamtso Rinpoche, maintained different lineages of "exegesis" of Shentong. However, it's not the case that it is a uniformly endorsed position in the Karma Kagyu, much less in any of the lineages that have incorporated other Jonang practices.
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