Because the postings against Edgar (and DH's in general) joining the Hall are predominantly from Cardinal fans, let me pose a hypothetical situation:

If the NL were to adopt the DH rule and the Cards decide to DH Pujols for the remainder of his career, should he be punished for not playing defense? I certainly don't think he should be punished by Hall voters; by letting a better defensive player take the field in his place he is actually helping his team.

Edgar is a similar situation; by simply hitting whenever it's his turn in the lineup he is giving the Mariners a better chance to win than if he would also play defense.