A serious problem, but it came out of the weird VatII "collegiality" doctrine. The popes were lax, but I'm not sure it was so much out of personal cowardice as out of a desire to conform themselves to this council (which was merely a pastoral council and did not/could not even issue anything binding).
You are correct. When you think about it, it becomes clear that an overemphasis on “collegiality” is probably the root cause to nearly all of the proliferation of heterodoxy over the last 40 years. Perhaps, in the “old days,” there was almost no consideration given at all to the legitimate concept of collegiality, but, in correcting that problem, the baby got thrown out with the bathwater. The end result has been chaos, with renegade and semi-renegade bishops dismantling doctrine and liturgical practices for decades now. Benedict clearly wants to rein in that sort of thing, but he must be consistent in the firm and decisive applications of his corrective actions.