Let me put this closer to home (for me).
My parents could not get married because my mother was not fully paid up in church dues (approx 3,800 dollars according to her).
They got married in a Protestant Church (My Dad's).
Mixed Marriage was another issue that reared it's ugly head.
My grandmother was also behind in her church dues (tighes if you wish) and could not be buried in a Catholic Cemetary until it was paid up.
The Catholic Church uses threats of Religious damnation to extract money from it's members not in "good standing", and that's not right.
By the way, I'm not Catholic.
I have been a practicing Catholic for most of my 34 years, and I'm very well read about the Catholic Church, especially the Church in the U.S.
And I can assure you that your mother's situation, which is undeniably tragic, is highly anomalous, and likely the result of a misinformed or misguided pastor, and in no way a general phenomenon.
By 1980, mixed marriages -- a marriage between a Catholic and a person of another person, performed in a Catholic Church or in another place, officiated or co-officiated by a Catholic priest -- we both completely legal, and not uncommon. If this particular pastor forbade it, then he was in error, and not in keeping with Church practice or praxis. I've been to three mixed marriage ceremonies, one in a Catholic Church, one in a Lutheran Church, and one in a ballroom of a country club co-officiated by a priest and a rabbi. It was a very moving ceremony.
And I've never once heard of tithing -- neither the word nor the concept (giving 10% of your income) -- used in a Catholic context. Not once. And if a pastor would refuse marriage to someone who had not paid off a pledge, he would be wildly (or deliberately) misinformed, and acting out of either ignorance or malice. And the same goes for being refused burial for non-fulfillment of a pledge. They're both highly anomalous situations and in no way representative.
Finally, I've never once -- neither in my personal experience nor in my wide reading -- heard of an example where "The Catholic Church uses threats of Religious damnation to extract money from it's members not in good standing." I've heard examples of evangelical protestant ministers going down that road, but never once a Catholic priest, pastor, bishop, or other official.
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The church has a track record of trying to affect policy of both local and national Government.
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Some examples are necessary for your assertion to have any validity.
I recall was one incident, leading up to either the 1980 or 1984 presidential election, where an American bishop said something along the lines of, "I can't see how a Catholic in good conscience could vote for a candidate other than Ronald Reagan" (and I'm paraphrasing). He was instantly condemned by both American Catholic officials, and by the Vatican itself.
But I suspect that's not what you are referring to.
Catholic pastors certainly do exhort their parishioners to let their lives and actions be guided by moral and ethical principles, and this can (and does) redound in everything from choosing candidates to support and vote for, to actions by individual Catholics to frame the public debate and influence the passage of legislation.
But, as American citizens, aren't they free to do precisely that, just like every other citizen? Should Catholics, as Catholics, be restrained from participating in public life and the political process? Catholics abound in American political life, and on both sides of the aisle, including the Vice President, Secretary of State, House Minority Leader (and former speaker), six of the nine Supreme Court justices, about 32% of the House and 28% of the Senate, etc., etc. Should they be proscribed from "trying to affect policy of both local and national Government"?
A dear friend of mine had a similar problem a number of years ago. She had belonged to a Catholic church all of her life (my church btw), graduated from high school and moved away to attend college. She graduated and worked for a few years in another state, met the man she wanted to marry and wanted to have the service back home. The priest wouldn't marry her unless she paid church membership retroactively from the time she left town. The priest figured out how much he thought she should owe and pretty much gave her a bill. Her family had been supportive of that church for years but they weren't going to be extorted. They found another Catholic church in a nearby town and brought in a Monsignor who was a family friend to do the service. It was the nicest wedding I've ever been to.