Clayman's whole argument was nonsense, though. He was the weak guy, who knew he's weak and thus tried to turn all the other older members against a strong newcomer, to maintain his own position (and pride). He had originally tried to use Rimuru as nothing but a tool for his own awakening, so it must have been quite a shock to have Rimuru appear in the demon lord organisation meeting as a true competitor.
Clayman also had another fatal flaw his own, personal weakness had brought about: He thought the demon lord association could be used as a tool for his own purposes as well, which is what this whole meeting was all about. He believed he could use the other demon lords to get rid of Rimuru. However, the other demon lords have no interest to do any such thing. If you are a demon lord, you sort out your own problems.
The only question mark is why didn't Clayman order Milim to attack Jura Tempest. It might be explained by his own history as a puppet master/manipulator. A direct attack in his mind is a lesser method than manipulating others to do his dirty work. On the other hand, his whole argument in the meeting was about Carion planning to attack him (in cooperation with Rimuru), so perhaps he thought if he appeared too aggressive himself, it would lessen his position. Another sign of his personal weakness and fear.