Worst-case scenarios are possible in any situation, and I think you're extending it to a worst-case scenario that's highly unlikely. There's been no bar on filing ethics complaints for the past 20 years, since the cabinet code was created and the almost two years since the MPs' code was created. You've only seen a dozen complaints in the past dozen years, so I don't see the danger, especially when it is libellous to make a false complaint.
On May 30th, 2006. See this statement in context.