A problem can be serious without being wide-spread, and this is a great example -- false accusations (of any crime), though rare, sow the seeds of doubt in the testimony of every accuser. Every widely publicized false accusation (Duke lacrosse rape, etc) causes hundreds or perhaps even thousands of real rapists to go free and rape more people, since jurors take the possibility of a false accusation as "reasonable doubt."

As with any crime, the evidentiary standard is "beyond a reasonable doubt" -- to convict someone for false testimony, you would need to conclusively prove that they did so willfully. This is already the law, the crime is called perjury -- it's just that the punishments are so mild that they are not serious deterrents. Imagine if making willfully false allegations of a crime was punished by twice the prison sentence of the crime being accused -- I bet one VC wouldn't try to poke another in the eye with a false sexual harassment blog post.