Fr. James Altman's recent video telling Catholics they cannot be Democrats is becoming a point of contention within the Church. It is a well produced video and in it he makes some very good points. For example, he is completely correct that the Church (in their bishops and priests) can and must have something to say about politics, political policies, and even at times positions of political parties. Bishops and priests can and should speak out against it when those governing pass laws or adopt policies that are intrinsically evil. They also should address the cases in which political parties adopt intrinsic evils as part of their party's platform (e.g. abortion). Fr. Altman also is correct in saying one cannot vote for a politician who promises to support intrinsic evils (e.g. abortion, redefinition of marriage, redefinition of the human person, coercive laws that violate consciences, etc.), at least this is the case when there is an alternative who does not promote equal or graver intrinsic evils.
However, Fr. Altman's makes several errors, of which he does not seem to be aware. While one may call into question the prudence of being a member of a party that has intrinsic evils as its party platform, being a member is not intrinsically evil. There is no Catholic teaching he can point to that says that. He can only assume that it follows necessarily from the correct premise against promoting the intrinsic evils themselves, but it does not follow. Just as one need not renounce his US citizenship because there are laws of the land promoting intrinsic evils (at least in the laws' normative interpretations), one does not need reject his membership in the Democrat party because of its platform. However, to stay one must not only resist politicians or efforts that promote the evils, he must work to overcome those intrinsically evil laws in one's nation and planks in one's party's platform planks.
Fr. Altman is not correct in saying that one may not vote for a Democrat. While there may be very few one can legitimately vote for, there are pro-life Democrats for which one may licitly vote. One may question the prudential judgment of those doing so when it could be counterproductive to the goal of avoiding promoting unjust laws and when there are other alternatives, but voting for a pro-life Democrat who promises to work to overcome the intrinsic evils in his party is not intrinsically evil.
Fr. Altman's approach is also damaging to the faith of Catholics who listen to him. He may make himself and others feel better, but he does not serve anyone well. His method is not likely to convince many of those he intends to reach. Rather than falling into the elitist error of telling Catholics how they must vote or what party they can and cannot belong to, we need to do the harder work of teaching the Church's moral/social teachings and the processes by which we can make the appropriate judgments ourselves. If we treat adults as teenagers, berating them and directing them to do something "because I said so," we should not be surprised when like teenagers, they dismiss us out of hand without actually listening. If we treat adults as adults and explain to them respectfully, not just the whats but he whys and hows, we might just be surprised to see at least a few rise to the occasion and begin to think rightly for themselves. Moreover, and perhaps even more importantly, fanning the flames of suspicion and revolt against the hierarchy which Jesus established to teach, govern and sanctify His Church does the work of Satan rather than that of Jesus Christ.
We can and should point out errors, even of prelates. But we must do so in the way Jesus taught us: go first in private, then take two or three witnesses, and then take it to the Church. We can warn others of the errors if bringing it to the Church still leaves the error publicly uncorrected, but no Catholic has the right to undermine faith of others in the offices of the Church which Jesus Himself established to guard and protect the faith. Rather than bursting spleens with displays that appear to fall into the temptations of destructive self-righteousness (and so can be dismissed as such), we need to have the courage and patience to do the thankless, slow and plodding efforts of transforming ourselves into Christ and then giving Him to those placed in front of us whom Jesus Christ put there to serve. We certainly undermine our credibility when we declare as true something that is not. Oversimplification of truths (which in this case have become errors) and taking the shortcut approach to providing lists of do's and don'ts is, in part, how we got to this point. It is not going to get us out of it.