The argument by those dinosaurs is, that MFP wants to rewrite article 112.
The MFP proposal, as far as I understood it, would only allow the Palace and its Royal members to file a "lèse-majesté" cases. That (yet to be formulated) revision would have to pass parliament, then presented to HM for His signature and then published in the Royal Gazette.
So all those hand-picked dinosaurs could no longer hide behind this "lèse-majesté" law, which has been grossly misused in the past by too many people to get rid of political or business opponents. A revision would result in the initial reason this law was created in the first place. So it is quite obvious, why all those misusers - outside the Palace - are against touching this delicate issue.