Catholics and Protestants are nothing less than the "whore of Babylon" whom the Lord denounces...
Joseph Smith History 1:18-20:
"My object in going to inquire of the Lord was to know which of all the sects was right, that I might know which to join. No sooner, therefore, did I get possession of myself, so as to be able to speak, than I asked the Personages who stood above me in the light, which of all the sects was right (for at this time it had never entered into my heart that all were wrong)—and which I should join." "I was answered that I must join none of them, for they were all wrong; and the Personage who addressed me said that all their creeds were an abomination in his sight; that those professors were all corrupt; that: “they draw• near to me with their lips, but their hearts are far from me, they teach for doctrines the commandments of men, having a form of godliness, but they deny the power thereof.” He again forbade me to join with any of them;..."
"And also those to whom these commandments were given, might have power to lay the foundation of this church, and to bring it forth out of obscurity and out of darkness, the only true and living church upon the face of the whole earth, with which I, the Lord, am well pleased, speaking unto the church collectively and not individually— For I the Lord cannot look upon sin with the least degree of allowance;"
Prophet Joseph Smith, Teachings of the Prophet Joseph Smith, Section Six 1843-44, p.375
"The old Catholic church traditions are worth more than all you have said. Here is a principle of logic that most men have no more sense than to adopt. I will illustrate it by an old apple tree. Here jumps off a branch and says, I am the true tree, and you are corrupt. If the whole tree is corrupt, are not its branches corrupt? If the Catholic religion is a false religion, how can any true religion come out of it? If the Catholic church is bad, how can any good thing come out of it? The character of the old churches have always been slandered by all apostates since the world began."
Official LDS Church Publication, The Seer, Vol.2, No.4, p.255
"Both Catholics and Protestants are nothing less than the "whore of Babylon" whom the Lord denounces... as having corrupted all the earth by their fornications and wickedness. And any person who shall be so wicked as to receive a holy ordinance of the gospel from the ministers of any of these apostate churches will be sent down to hell with them, unless they repent of the unholy and impious act.
If any penitent believer desires to obtain forgiveness of sins through baptism, let him beware of having any thing to do with the churches of apostate Christendom, lest he perish in the awful plagues and judgments, denounced against them. The only persons among all nations, kindreds, tongues, and people who have authority from Jesus Christ to administer any gospel ordinance are those called and authorized among the Latter-day Saints. Before the restoration of the church of Christ to the earth in the year 1830, there have been no people on the earth for many generations possessing authority from God to minister gospel ordinances. We again repeat. Beware of the hypocritical false teachers and imposters of Babylon!
In the Book of Mormon, there are many references to "a church which is most abominable above all other churches." This church had a history of an Inquisition similar to the Roman Catholic Church in that it "slayeth the Saints of God, yea and tortureth them and bindeth them down, and yoketh them with a yoke of iron and bringeth them down into captivity" (1 Ne. 13:5). The people involved with this depraved organization wore finery similar to priestly vestments; their church structures were ornate; and women in their church, like nineteenth-century Catholic nuns, were accused of sexual misconduct.
Nephi reported in the Book of Mormon that he "saw gold, silver, and silks, and scarlets, and fine twined linen, and all manner of precious clothing; and I saw many harlots" (1 Ne. 13). The Book of Mormon also predicted the Catholic Church's sale of indulgences. "Yea, it shall come in a day when there shall be churches built up that shall say, come unto me and for your money you shall be forgiven of your sins" (Morm. 8:32)
The Book of Mormon also asserts that this abominable church "whose foundation is the Devil" and who is "the whore of all the earth" would pervert the scriptures entrusted to people by God. A book was to come from the Jews which would contain the gospel. The BoM also states this book (the Bible) eventually would fall into the "hands of the Great and abominable church" after which are "many plain and precious things taken away from the Book" (1 Ne. 13:26-29).