church discipline and politics OR what does it take to be/remain a member of a group?

From Richard John Neuhaus in First Things...

The question is what is to be done about public figures, usually politicians, who have publicly, flagrantly, and persistently violated their communion with the Church by supporting the unlimited abortion license. The question continues to agitate Catholics and attract the attention of the media. It could hardly be otherwise. The Church holds that the Eucharist is the “source and summit” of the Church’s life, and receiving the body of Christ is the deepest expression of communio with the body of Christ, the Church. When a public figure rejects and opposes clear teaching on faith and morals and then receives Communion, as though such rejection and opposition is no big deal, the result is public scandal and confusion about whether the Church really means what she teaches. In this unhappy state of affairs, many bishops are complicit....

The difference is not between hard-line and soft-line bishops, with the former depicted as legalistic and punitive and the latter as pastoral and compassionate. The difference, rather, is between those who do and those who do not evidence a bold devotion to the teaching and pastoral practice of the faith....

When and how to practice "church discipline"-- as prescribed in the Scriptures? A difficult question whose answer typically errs on the permissive side for a variety of unfortunate practical reasons.

This also speaks to a broader issue: to what extent can one disagree with the premises of group X while still remaining a (faithful) member? Here, can one be a pro-choice Catholic? Can one be a Christian and dispense with doctrinal issues A, B or C-- or practices D, E, or F-- or endorse behaviors G, H, and I? Can one be a anti-union Democrat, a pro-gun control Libertarian, or a anti-business Republican?