The Conservative Party is supposed to be a democratic organizations where the members chose their leader, not a top-down elitist club
The Conservative base, made up of party members, should decide who wins the race. If people want to vote for Decaire, they should be free to do so, and if they want to vote against him, they should be free to do so as well.
But banning him would be totally anti-democratic. If the Conservative Party elite are confident that he doesn’t speak for the party, then let him run and let the members prove he doesn’t represent the party.