In the TBC, the order is neither monastic nor lay. I think that comes from Sangharakshita's observation that "good monks" who followed the rules could be rather uninspired, and "bad monks" who didn't exactly follow the rules could be very inspiring and do lots of good in the name of the dharma.
Literalism is also seen as a big hinderance in the spiritual life, and the rules seem all about literalism.
Finally, the idea that all 5 monks who ordain a monk are pure in their observance all the way back to the Buddha is absurd. Someone in there has to have done something unpure, and therefore the idea of purity back to the Buddha can't be true. Anyway, maybe it's more of an aspiration than an actualization, but even so, the language is not true.
Along comes a free updated version by Thanissaro Bhikkhu free on their lovely website.
There is a kind of scholasticism that feels more academic than spiritual, but I appreciate the Theravadans for their translations of the primary texts, and their commitment to the early cannon.
Supposedly the Vinaya came about because a monk named Sudinna, was asked by his family to provide an heir because they were afraid their lands would be taken away. Even though he had renounced the worldly life and become a monk, where sexual intercourse is forbidden, he chose to sleep with his wife 3 times to try and provide an heir. Perhaps he thought it was a kindness to give his family an heir.
In the legend of the Buddha he hangs around until he's given his father an heir, then he goes off on his journey. I wonder if he's expressing his feeling that he shouldn't have done that. Some people think the legend of the Buddha's life is a story, and that the Buddha was always a spiritual monk.
The Buddha tells him a list of negative places it would be better to put his penis. You can find the list for yourself. He expresses himself strongly.