Dear Sam,
Your funny anecdote about tosefta kifshuta being on a seforim shelf has been verified many times. It was known (can’t verify it for modern times) that many serious yeshivas had it on the shelf without making a fuss about it. Most people learned it without knowing they were supposed to have first dissected the hashkafic kishkes of the author.
But I’d like to go back to Rebbe yid’s comment to me above. If we get past the ignorance and adolescent kana’us of the comment, it represents a legitimate point of view. Many yeshivishe hold that emes can only be brought forth from a kosher source, and one must avoid any contact or even appearance of it with one deemed a “rasha (sic)”. This is a legitimate point of view.
The other side, held by many if not most world class lamdanim, is that emes is emes no matter who says it. They may or may not feel comfortable learning R’ Lieberman’s scholarly works, but they know genius when they see it, and their intellectual drive and thirst for truth far outweigh any possible hashkafic discomfort. For the ones who avoid it at all costs, one can’t help but feel for them, their depth of understanding will necessarily be compromised. But my feeling is that the abstainers are a small minority.