Separation of Church and State

It seems that at least one Cardinal in California has taken it upon himself to devote a sermon to the subject of the illegal immigrant debate. One of the parishoners, who was visiting from Ohio (I believe) said that the Cardinal had no right to use his sermon for such a call, that the sermon was somehow a violation of the principal for separation of church and state.
Now, from my quick read at the First Amendment Center (click on the link above), it seems that the initial intent of this principal was to keep government from dictating the regligious beliefs of the nation. From that point forward the separation of church and state has been a grey area.
Cardinal Mahony made the point that as a christian he could not support any laws that would make it more difficult for people to emmigrate to the United States, nor could he support any laws that would make life more difficult for the illegal immigrant population already in the U.S.
This is his opinion. He has every right to express it. Because he chooses to express this opinion to his congregation during mass, is that some kind of violation of the C&S principal? Or is the line not crossed until he uses his power as Cardinal to influence someone in political power? (Much like the time when presidential hopeful John Kerry was denied communion because he was not a firm supporter of anti-abortion legislation.)
How much of a violation of the C&S principal is that? Can the church keep track of every parishioner who does not hold fast to the convictions of the church? By denying communion was the church hoping to reverse Kerry's stance?
The church itself has rights to its beliefs, and even if I don't agree with the stance I won't deny the institution its rights and opinions.
But again, when does that line between C&S get crossed? When does opinion become political influence? How much conflict is generated when religion influences a political decision? Even without having talked to anyone I can guarantee that there are people who vote, everyday-citizens who vote, based on how the results of the vote will integrate with their religious beliefs. Can we then blame those citizens of a violation of the C&S principal?
And who on earth would keep track of all that?
It would be wonderful if the argument were as simple as "The first amendment states that no government shall dictate the religion of its people" and we could all leave it at that. But with every individual comes opinions and beliefs that shape decisions. And one starts to bleed into the other; and we question the rights of a religious leader to forward opinions when that opinion may not have any influence on the outcome what-so-ever. And we question the morals of those who don't base their opinions entirely on belief; labeling them as some sort of aberration who never had a church to separate from a state in the first place.

Well, lunch is over. Another half hour spent musing on subjects I don't know nearly enough about.