Why has the Qur'an been around for almost 1500 years?
Lies are eventually exposed to be lies. Mark Hofmann was so clever in his document forgeries that he deceived both LDS and RLDS historians, and also document experts. Yet his forgeries are now known to be forgeries, while he rots in prison for killing people who were on the brink of exposing his deceptions.
If the witnesses lied, or conspired to lie, such deception would have long ago been revealed. The fact that most of the witnesses became estranged from the church that published the Book of Mormon containing their testimonies would surely have caused one or more of them to tell about any deception that they had engaged in. The fact that all eleven of them remained true to their printed testimonies, despite frustrations and disappointments regarding the publishing organization, is overwhelming evidence that they had not engaged in deception.
As they lived their lives, some of them were approached by persons who knew of their estrangement and wanted to get them to admit to deception. The most interviewed witness was the last surviving of them: David Whitmer. If any of the ten who had died before him had confessed to deception, the game would have been over, and there would be little need to interview him. But none of the previous ten had ever confessed to deception. Therefore, David Whitmer was badgered and hounded by persons eager to not allow the last remaining witness to die firm in his testimony. Yet he did die firm in his testimony.
This leaves enemies of the Book of Mormon in a pitiful condition regarding the witnesses. It means that they have to invent a new standard to judge by: refusing to believe the printed testimonies unless they are backed up by other statements by the individual witnesses. This is a false standard, because it tries to diminish testimonies made "with words of soberness" while inflating more casual comments.
An 1828 revelation through Joseph Smith has this warning: "Verily, verily I say unto you, Woe be unto him that lieth to deceive, because he supposes that another lieth to deceive, for such are not exempt from the justice of God."
What I take that to mean is that even though you may think that people have lied to deceive, that is no excuse for you to lie or quote lies about them. Investigating the Book of Mormon Witnesses by Richard Lloyd Anderson should be required reading for anyone wishing to criticize the witnesses without quoting lies about them in the process.