Anabaptists and the pope

I believe so. The Anabaptists joined the Protestant movement readily enough, even though they had been heretics to the RCC. The Reformers also rejected the Anabaptists, but this did not diminish their part in the Reformation. Of them Luther wrote that they predated the movement, were among them but not a part of them (that they were truly heretics because of their doctrines...specifically baptistic doctrines, although they also held additional beliefs that departed from Reformed doctrine). This is why it is misleading to refer to these Christian groups as not being "Protestant" (although not belonging to the RCC, they still protested the RCC and joined along side...for a time....the Reformers). If it were not for Zwingli and his rise, we may be able to say that they merely took advantage of the Reformation to start another. A major difference, IMHO, was that Anabaptist doctrine was not conducive to secular governmental form where as the RCC and the Reformers shared a misguided and pagan notion of Christendom.

 

As a rule, Anabaptists were not quite so vituperative as the magisterial reformers, and not so personally abusive, but the sentiment you have mentioned was common.

To quote Sims at length:

In the third place, when I think of finding an unblamable church without spot and blemish, which serves the Lord with all its power and which conforms itself to his word - I verily find such an ungodly, abominable, corrupted and confused people; so carnal, idolatrous, whoring, cruel, ungodly, unbelieving, ignorant, blood-thirsty, unmerciful, drunken, pompous, luxurious, proud, avaricious, greedy, envious, adulterous, false, deceiving, sodomitic, refractory, disobedient, rebellious, vain, and so devilish, that a godfearing soul must stand dumbfounded and be ashamed thereat. Yet they claim to be the true bride, the believing church of Christ. O no, dear reader, no. Christ Jesus does not own such a bride or church. But his bride is flesh of his flesh and bone of his bone, Eph. 5:30; she conforms to him, Rom. 8:29; is created after his image, Col. 3:10; partakes of his nature, 2 Pet. 1:4; is minded as he is, Phil. 2:5; seeks nothing but heavenly things where Christ Jesus is, sitting at the right hand of his Father, Col. 3:1; yea in God's church nothing is heard, seen or found but the true doctrine of our beloved Lord Jesus Christ and his holy apostles, according to the Holy Scripture. But in the beforementioned churches it is mostly doctrines, flatterings, comments, councils and commandments of men. Here is faith, truth, obedience, baptism of the believing, according to the word of God, true fraternal love, and the service of our neighbors; yonder is unbelief, falsehood, disobedience, infant baptism without God's word, hatred, envy, tyranny, cruelty, shedding blood, quarreling, lawsuits, backbiting, cheating, stealing, robbing and murdering; here is teaching, admonition, consolation, reproof in righteousness - there, mere corruption, heresy, upbraiding and slandering; here, blessing, praise and thanksgiving - there, cursing and swearing by the suffering of the Lord, by his wounds, sacraments, flesh, blood and judgment; here, longsuffering - there, inflammable temper; here, humility - there, pride; here, mercy - there, mercilessness; here, true religion - there, idolatry; here, spirit and spiritual wisdom - there, flesh and foolishness; here is prayer in spirit and in truth - there, mockery with many powerless words; here is prayer for the Lord's truth - there the righteousness of the Lord is persecuted; here is faith in Christ - there, idolatrous ceremonies; in short, here is Christ and God - there, anti-christ and the devil.
-- The reason why I, Menno Sims, have cause to teach and write (1542)

Or a portion of a 1521 letter from Hubmaier to humanist scholar Johannes Sapidus in which he refers to Pope Leo X (the Dancer of the City) as the Antichrist:

"Christ avoided earthly governments; the Dancer of the City emulates these governments.
Christ, he wears a crown made of three thorns.
Christ washes feet, and the kings offer him kisses.
Although money loosens the clergy’s grip, Christ drives out all the clergy.
Christ presented himself as a servant, but the Antichrist publicly displays himself as lord of the world.
The former bore the cross; the latter emerged from an avaricious servant.
Christ comes meekly; the Antichrist comes in superiority.
The former is without money; the latter controls all the governments of the world.
The Antichrist has been offered their laws, a Dancer who absolves iniquity.
The former drove the merchants from the temple, but the latter accepted the merchants.
May Christ ascend, but may Pluto descend to hell."
(Even The Catholic Encyclopedia acknowledges that Leo, a Medici, "paid no attention to the dangers threatening the papacy, and gave himself up unrestrainedly to amusements, that were provided in lavish abundance. ... Even during the troubled years of 1520 he took part in unusually brilliant festivities. Theatrical representations, with agreeable music and graceful dancing, were his favourite diversions.")

 

Often, while this may not have been the only difference, it was the cause of persecution. But you also have to remember that the Reformed and the RCC shared a common understanding of the nature of the Church ("Christendom," a church-state) so baptism was more than a personal matter of redemption (either sign or mode). "Believers Baptism" was contrary to Reformed faith (historical...not "Reformed" as used today) - which was, BTW, an issue that Zwingli realized when he ultimately denounced Believers Baptism in favor of a Reformed structure.

 

Unfortunately this was also a part of Reformed doctrine of the Reformation. They did not completely rid themselves of RCC error when it came to understanding exactly what the Church was to be.

It is interesting to note that the term "Anabaptist" (and you are right that it was a diverse group) was coined by adversaries of that group to identify them as "re-baptizers." Perhaps it was simply because this was a common practice, and certainly it was not the only "heresy" they believed, but simply holding to "believers baptism" was enough to merit condemnation by both the Reformed and the RCC.