I've been very disturbed by the actions of various religious lobbyists on the political stages of the world in recent years.
Whether we are talking about the Pope denying communion to "pro-choice" politicians, or the insane howlings of lobbyists like Peter LaBarbera, there is a fundamental underlying behaviour here - that of the bully.
Bullying depends upon the existence of a threat, occasionally reinforced by some kind of implementation of that threat in some way. Bullying depends upon a degree of public humiliation in order to be effective.
When clergy stand up and publicly talk about denial of communion to politicians who fail to tow the line put forth by the clergy, they put on the public stage two threats. The first threat is to the "immortal soul" of that politician. For some, this will be a significant threat by itself, but the more important aspect is the threat of public humiliation that is carried by making the declaration so publicly. The threat is in fact twofold, and is designed to coerce people to a particular line of action regardless of the political and legal realities.
While the Pope may worry about "relativism", one has to question the validity of any argument put forth but supported primarily by means of forceful coercion.