John 14:15 "If ye love me, keep my commandments."
But in this you are ignoring the command of the apostle to make necessary and critical judgements:
1 Cor 5:11
"But now I am writing you not to associate with anyone who claims to be a brother but is sexually immoral or greedy, an idolater or a verbal abuser, a drunkard or a swindler. With such a man do not even eat. 12What business of mine is it to judge those outside the church? Are you not to judge those inside?"
And there are other commands refraining from divisiveness:
Titus 3:10 "Warn a divisive person once, and then warn them a second time. After that, have nothing to do with them. 11 You may be sure that such people are warped and sinful; they are self-condemned."
The history of Christian dominations from the Council of Chalcedon is that they are divisive because distinguished on philosophical and political principles. Thus it was the Roman Catholic church excommunicated all other denominations after the Council of Chacedon in AD 451 except Eastern Orthodox because they would not accept the hypostatic union of two non-blendable persons (or natures) within Christ to form one person, equally God and equally man.
The (heretical) Nestorian principle of perceving the humanity of Christ, and restricting the divinity of the human Christ to his being the "face" of God, was precluded. Nestorians went on to evangelize Asia and the east. The divisiveness of the Roman Catholic church in respect to Nestorian "heretics" is one of the primary reasons why Islam exists in the world at all. Were it not for this opposition, Islam would have been wiped out in the 13th century or before. In fact Catholics would rather abide muslims than Nestorians.
Why then should the Catholic hierarchy be seen as axiomatically Christian? Their anathemas are dished out on other Christians but no longer on muslims. They need to prove their Christianity as much as anyone else.
Transubstantiation is another highly divisive principle, where it is obvious that the tokens of bread and wine are used figuratively so as not to imply metamorphosis. There are many others, such as in permitting ladies not to cover their heads in church, which was condemned by Paul in 1 Cor 11:1-16. This heretical practice is now allowed both by Catholic and Lutherans.
For all these reasons, a Christian can bring another into judgement.
I would not go that far. But a Catholic may not be a christian if the only evidence of faith lies in the holding of philosophical positions. Many Catholics suffer from a lack of faith but in this I do not single out Catholics from others.
Whether they are serious about obeying Christ's commands, which would include being seen to refrain from polluting the doctrines of Christianity with man-made teachings rooted in human philosophy, and in human politics. To these things not only Catholics but many others are increasingly prone, but equally members of most denominations can refrain from such to prove themselves a Christian, although some denominations are quite beyond the pale of orthodoxy now.