If you apply the "innocent until proven guilty" principle, it's not a bad idea. It should be proven that the accuser lied to get condemned. I would expect this to happen not that often - basically never when it's just "my word against your word" - but it would create a big risk for those who are rationally plotting to launch a false accuse - in the unlikely but possible case that evidence is found that they willfully lied, eg if there was a witness they didn't know about, if there was a recording of what happened, etc.