[NYer]

They are claiming Vatican II is tainted and invalid because Archbishop Lefebvre signed it?

No. As the article states: "traditionalist propaganda spread the belief that Lefebvre had always opposed the documents. The original copies of the Vatican II documents show the contrary and for many this has come as a surprise."

[nickcarraway]

But if Archbishop Lefebvre signed it, will that lead everyone to question the legitimacy of Vatican II?

(Personally, I don't understand this: I had always heard from all sides that he had signed off on it.)

[narses]

"traditionalist propaganda spread the belief that Lefebvre had always opposed the documents. The original copies of the Vatican II documents show the contrary and for many this has come as a surprise."

That appears to be a made up thesis, evryone I know in the SSPX communities know that the Abp. signed all (save two) of the documents. The issue was the use by the heretical Modernists of the so called "Spirit of Vatican II" to suppress the Latin Mass and the Traditional elements of the faith in pursuit of a changed NewChurch.