Against...
Yes, but still, it should ultimately be up to the organizer alone to decide whether to accept or not. The presence of a WMP, IMHO, should simply indicate that there was cheating, but everyone should decide for themselves whether to play or not... After all, it could also happen that someone is given a WMP, and someone else disagrees with the AC's decision and wants to play them for rating. I think that deciding whether to play or not, whether to include in a tournament or not, should still be up to each individual, regardless of the WMP.
Added after 4 minutes
What's the point of the WMP at all then? After all, even without it, you could simply not include them in tournaments, not count rating games, and consider tournaments invalid if their holder participates. I am against it... In my opinion, it is merely informational. You could, of course, forbid holders of a WMP from playing each other, so they don't accumulate rating that way.
Option 2 - Player A is playing a playoff match in a tournament against Player B; Player B egregiously cheats during the game (obvious maphack and proven save-file snooping) and wins; Player A appeals to the tournament organizer, but the organizer is stubborn — even if a WMP is issued, Player A is eliminated from the tournament.
Both situations are quite real and have already occurred on HeroesWorld. The poll is necessary and essential.