Roman Catholics view the landscape of modern Christianity and see chaos. Multiple denominations, multiple churches. I also deplore the current state of affairs, but unlike Rome, I do not agree with their solution.
Their solution is of course follow the Pope. This is what they mean by unity, all following the Pope. The Reformers viewed the pope as an anti-Christ, because he took authority that properly belonged to Christ alone. (using the more common meaning of anti-Christ) Before you get too shocked at the statement, I would read "Pope" Gregory I's comments below. I would like to submit for your consideration that the papacy is one of the main causes of disunity. Furthermore, the papacy was not present in the primitive church.
Catholic apologists have tried many times to establish papal authority, but I believe the following quotes completely disprove that contention.
Cyprian (200-258): Neither does any of us set himself up as a bishop of bishops, nor by tyrannical terror does any compel his colleague to the necessity of obedience; since every bishop, according to the allowance of his liberty and power, has his own proper right of judgment, and can no more be judged by another than he himslef can judge another. (Seventh Council of Carthage, paragraph 1)
In canon 6 of the Council of Nicea (325 AD) it was declared that each church center was to be ruled by its own bishop and not by one head over all bishops.
In canon 28 of the Council of Chalcedon (451 AD) it was declared that Rome's rank was based on its political significance rather than any spiritual superiority.
Gregory I, bishop of Rome (540-604): None of my predecssors ever wished to use this profane word. For clearly if one patriarch is called "universal," then the name "patriarch" is taken away from the rest....To consent to this wicked word is nothing less than to destroy the faith....It is one thing that we should preserve unity of faith; another, that we ought to repress self-exaltation. But I say it confidently, because whoever calls himself "universal bishop," or wishes to be so called, is in his self-exaltation Antichrist's precursor, for in his swaggering he sets himself before the rest. (Epistle 18, emphasis mine)
So the traditon of the papacy is contridicted by tradition. I encourage all those wishing a more detailed examination of early church government and related issues concerning Rome to read Calvin's Institutes book IV, chapters 4-6.