Protestants will claim that the HS helps guide us, but it’s a very rare Protestant that will claim divine protection from error.
I used to listen to the sermons of Dr. James Kennedy, a pastor of the Reformed (Calvinist) Church. He very much insisted that the practice of homosexuality and “gay marriage” are sinful. But then, I became aware that certain Protestant denominations (Episcopalians?) disagree, and ordained a Bishop who is openly gay. At this time I also wasn’t sure that the Catholic Church has got it right (the CC of course says what Dr. James Kennedy the Reformed Church’s pastor says). And I felt very uneasy about not being able to know God’s will for sure. I used to have two colleagues, both very nice guys, both practicing gay men. I wasn’t going to bring up the subject, but if any of them did, and asked for my opinion, what could I say to them? I could only say that according to some Christians, God approves of homosexuality, but according to others, God regards homosexuality as a serious sin. And if I personally take the opinion that practicing homosexuality is wrong, while God approves it, then I am guilty of bigotry and creating divisions among Christians. But if I say that the practice of homosexuality is perfectly acceptable from a moral standpoint, while in fact God condemns it, then I risk the sin of misleading people who may want to discuss the subject with me, and I risk causing (in part) their destruction, by encouraging them to sin.
What I want to say is that I realized, these things are not without consequences. It was imperative to find out, if possible, who’s on the right side of issues and who’s in error.
By listening to many Protestant ministries, it sounded to me as if, in their opinion, the Church is everywhere you can find Christians believers. That is, the Church is present in the Reformed Calvinist community that rejects homosexuality, and the Church is also present in the Episcopalian community that accepts and embraces homosexuality as a morally legitimate form of diversity.
In contrast to the Protestant understanding of what the Church is, the Catholic creed says that there is ONE Church (which, according to Catholic belief, is the Catholic Church), and true (error-free) teaching can be found in this ONE Church. OK, more exactly, the Church is one, holy, Catholic, and apostolic. It’s a visible organization that’s easy to find, even geographically and physically. And the Eastern/Oriental Orthodox, and Protestant Churches (or Protestant Faith Communities, more exactly) are not part of the one, holy, Catholic and apostolic Church which is error-free and which has the fullness of truth. However, according to Catholic understanding, the other Churches and Faith Communities do possess part of the truth, mixed with errors, and they are in a less than perfect communion with the one, holy, Catholic and apostolic Church established by Jesus Christ.
Unless you seriously believe the only Christians in the West are Catholics and everyone else has apostasized, Christianity in the West is very much divided and the East is very much unified by comparison.
According to Catholic understanding, Catholics are not the only Christians in the West. But only the Catholic Church, through its Magisterium and Bishops in Communion with the Pope, teaches the faith correctly. Any Christian, be they Catholics (baptized members of the Catholic Church) or non-Catholics, will risk making erroneous judgments if they do not hold fast to what the Catholic Church teaches, through its Magisterium and Bishops in communion with the Pope. Catholic and non-Catholic Christian believers, even Catholic Bishops can fall into error, if they choose to disagree with the Pope and with the Magisterium.
As a side note, Christianity is also divided in the East. There are the Catholics in the East, such as Melkite, Maronite, Syro-Malabar and other Catholic Churches, who are in full communion with each other and with the Roman CC. Then, there are the non-Chalcedonian Christians (including Armenians and Copts), also called Oriental Orthodox, who rejected certain dogma about the nature of Christ at the Ecumenical Council of Chalcedon (5th century), and broke communion with the rest of the early Church. After the Schism of 1054 (Catholic - Eastern Orthodox), the Oriental Orthodox such as Armenians are out of communion with both the EO and the C Churches. The Coptic Church came into communion with the CC in the 1960s, but not with the EO. The situation is actually way more complicated than what I describe here, because there are also other Christian Churches in the East that are out of communion with either the Catholic, Eastern Orthodox, or Oriental Orthodox Churches. Someone who traveled to Damascus, Syria, said that you can find a plethora of churches (as in church buildings), at every street corner, and it’s almost an impossible task to catalogue the number of Churches (as in Church organizations) these churches (church buildings) represent, as well as who is in communion/out of communion with whom at any given time. Just to give an interesting historical snippet about the divisions within Eastern Christianity, the Patriarch of Moscow (largest EOC, population-wise) broke communion at a certain point in the 1990s with the Patriarch of Constantinople (whom many EO regard as being at the place of highest honor among EO Patriarchs), but later they resolved their conflict that prompted this drastical measure from the Russian side, and they came back into communion with each other.
Imagine Metropolitan Jonah of the OCA Orthodox coming and preaching to a bunch of evangelical Anglicans at the ACNA kick-off event to drop women’s ordination, drop Calvinism, and dump the filioque and they all look at each other with a big grin indicating, “yeah…sure!” 
