If a person professes the Faith with us in the official Creeds of the Church, receives the Sacraments in communion with the Church, and takes part in the Liturgy of the Church, we are supposed to assume his orthodoxy and accept him as a Catholic without qualifiers. He may not be a perfect saint, and maybe he can't explain the difference between the Virginal Conception and the Immaculate Conception, but we ought to give him the benefit of the doubt.
The problem, of course, is that many people have been severely burnt many times by things that went masquerading as Catholic, when they were in fact nothing of the sort. And such people (and this goes for "liberals" as much as for "conservatives") will band together, circle the wagons, and try to keep from being hurt again. To do this, they will sometimes make pre-emptive strikes on people and groups they perceive as threats. And labels are the best way for them to distinguish who's who on the battlefield. It may not be excusable, but is at least understandable.
How to overcome this?