When Protestants disagree, they throw out the baby with the bathwater

Lutero:
But why does Rome never offer infallible clarification?

It offers infallible clarification continually. You and all Protestants object those infallible pronouncements, remember.

And if the magisterium ever got around to having a "final say", well, that would not guarantee uniformity of interpretation.

A final say? Everyone will have their final say on the Last Day. In the meantime, the Church is an ongoing business created by Jesus Christ to do His work in the world until that Day comes. Until then, There will be continual teaching in obedience to Jesus Christ.

If the original teaching is not necessarily perspicuous,

It isn't. Scripture says:
2 Peter 3:16

King James Version (KJV)
16 As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.

Do you know better than Scripture?

then nor is the clarification.

That depends upon the reader. If the clarification is not clear enough for some, it is clear enough for others. But even for those for whom that clarification is not perfect, the Church is still here and will produce more clarifications and explanations.

Sure, Protestants disagree... but so do Catholics.

Again, in a fundamentally different way. When Protestants disagree, they throw out the baby with the bathwater and start an new religious group. 

When Catholics disagree, they remain in submission to the Catholic Church. 

The common way the argument is phrased is along the lines of "but Scripture is so terribly hard and complicated, weneed an infallible interpreter!"

What does Scripture say? Why do none of you ever confront these verses? You keep saying that Scripture is easy and perspicuous, but Scripture doesn't say the same. Scripture says:
2 Peter 3:16

King James Version (KJV)
16 As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.

Does "hard to be understood" mean perspicuous to you?

This glosses over the fact that is was written by average men to be understood by their audiences. Paul wrote his letters with the fullest intention of being understood, but Catholics must think he was wasting his time: "There's no way the good folk in Corinth would understand! Scripture is so difficult!" The second flaw in the argument is that it doesn't address how exponentially more esoteric magisterial teaching is. There's no way that you can look at the Bible, and then at a library full of obscure Latin teachings of speculative theology, and say with any honesty that Rome has made a hard thing simple. It patently obviously hasn't. There is no epistemological advantage in being Catholic, because ultimately you also only have private judgement. The unity that Catholicism proposes is nothing more than a veneer that hides what people actually believe.

There is every epistemological advantage for the Catholic. Confront 2 Pet 3:16. Show me where it says that St. Paul's writings are easy to understand, as you claim.

And then, address this verse which says that people need guidance in order to understand the Word of God:
Acts 8:28-31

King James Version (KJV)
28 Was returning, and sitting in his chariot read Esaias the prophet.
29 Then the Spirit said unto Philip, Go near, and join thyself to this chariot.
30 And Philip ran thither to him, and heard him read the prophet Esaias, and said, Understandest thou what thou readest?
31 And he said, How can I, except some man should guide me? And he desired Philip that he would come up and sit with him.

Show me your epistemological advantage. I want to see the Scriptures which overcome these and speak your point of Scriptural perspicuity.

And I deny that truth has to be dictated. 

What does that even mean? 

The fact is that God revealed the Truth of Jesus Christ through His Church. Amongst those things He revealed is that we must obey His Church. If you want to deny this truth, it is your problem. Not ours. If you want to consider this "dictation", that is your problem. However, we love God and therefore, we obey.
Hebrews 13:17

King James Version (KJV)
17 Obey them that have the rule over you, and submit yourselves: for they watch for your souls, as they that must give account, that they may do it with joy, and not with grief: for that is unprofitable for you.

(continued tomorrow)