Ah, we can't avoid evil, or determine where catholic tradition is without making illicit judgments or rendering our opinions binding on others. I'll be waiting for an "authority" on that one.
You can and must avoid heretics. See St. Paul on this one.
As far as I can tell, you shouldn't be avoiding other Catholics because of doctrinal matters less than heresy. You do not shun excommunicants unless they are excommunicated by name and "to be avoided".
Heresy is part of the equation here because certain notions are in fact proximate to heresy and lead to heresy, as well as other factors that have destroyed our supernatural religion. Some certain doctrinal matters may not be heresy strictly speaking, but do have effects which destroy nonetheless and consequently should be avoided. Add to this a certain materialism and worldiness that isn't limited to a certain person or group of people and we have a terrible problem. As was said before, our material separation from the normal structure of the Church is accidental and beside our formal intention of adhering to tradition. This is, I believe, the proper attitude to have.
Materialism and worldliness have always been there. Heresy and error has always been there.
Material separation from the normal structure of the Church?
Here's a definition of the Church Militant:
"The assembly of men bound together by the profession of the Christian faith, and by the communion of the same Sacraments, under the government of their legitimate shepherds, and especially that of the one Vicar of Christ on earth, the Roman Pontiff."
(De Ecclesia militante [On the Church Militant], bk. 3, ch. 2, par. 9) (Pragae, 1721, II, p. 65a)
Do you see the problem, Caminus?