Greek was used throughout the Roman empire, much as Latin was used throughout Europe in the middle ages. Issac Newton wrote his Principia in Latin. Does that mean he was from a "Latin speaking area"? No, of course not. A philosopher, historian or scientist in England could discourse with the literati in other countries by this means. Latin was the international language of the middle ages, much as Greek was in the time of Jesus.
Actually, Latin was the language of the Roman Empire. Greek may have been read and spoken by the educated, but it certainly doesn't imply one was a Roman citizen. It implies simply that he was educated.
Paul doesn't just know Greek, but has complete mastery of the language. This fact shines through even in translation: look at the stophe/antistrophe/epode structure of his rhetoric. He has been educated to the highest level possible. Typical of a Roman citizen.
No, it would be typical of an educated citizen. Now, Paul's mastery of the language is questionable. In many of his letters, he admits to not even writing them, but having a scribe copy them. More so, when he does write, he brings attention to just how poor his handwriting is. I would take those two clues as to him not having a complete mastery of the language.
And again, it does not even begin to suggest he was a Roman citizen. All of the books of the NT were written in Greek. The Gospel of John is some pretty good Greek as well. That hardly means they were Roman citizens. It only means that they knew Greek, and were educated in it. And it wasn't only Roman citizens who were (and not all Roman citizens could read and write Greek anyway).
There is more circumstantial evidence. Paul urges his followers to pay their taxes, because the rulers are appointed by God himself. Everybody knew he was talking about the Roman empire. He actually called them "ministers of God"! What a suck-up! Paul did not oppose the Roman authorities in any way. In fact, the subservient nature of his doctrine actually helped Roman power. Why do you think these documents were allowed to circulate?
Jesus also tells his followers to pay their taxes. Certainly Jesus wasn't a Roman citizen.
More so, Paul obviously did oppose Roman authorities as he was thrown into jail multiple times, and was beaten by the authorities on a number of other times. So yes, he does show opposition to the authorities.
But of course Paul was talking about the Roman Empire in general. That is simply because he was addressing congregations that existed in the Roman Empire. He also planned on going to Spain, and most likely would have repeated the same sort of message, even though it wasn't part of the Roman Empire. So your argument really is weak at best.
Finally, as for the circulation of this material. We don't know how much it really even circulated at first. But just because it was circulated at all didn't mean that the Romans liked it. The Book of Revelations, which contains a lot of anti-Roman rhetoric, also circulated quite a bit. The Gospels, none of which were written by Roman citizens, also circulated quite a bit, even though they contain some anti-Roman ideas. Jewish works from that time, again not written by Roman citizens, circulated as well, even though some of them contained anti-Roman ideas.
So your argument really doesn't have a leg to stand on when other examples are examined.
Very circumstantial, I admit. It is possible to be an agent of the emperor, like Paul, and still not be a full citizen. All I have really shown is that Paul was a sympathizer or appeaser of Roman power. A freedman could rise to the highest circles of power, like Epaphroditos, secretary of Nero, without legally enjoying the full privileges of citizenship.
You just made a huge leap. Paul was not an agent of the emperor, and you have made no argument for that. You simply jumped to such a conclusion on what I assume to be a desire for it to be so.
So we have two pieces of circumstantial evidence: his complete mastery of Greek, his outright sympathy to the Roman cause. The notice in Acts which indicates that he was a citizen becomes a little more convincing in light of these circumstances.
Those two circumstantial pieces of evidence are not actually circumstantial. They have nothing to do with Roman citizenship. And he hardly had sympathy for the Roman cause.
I know that Acts is completely unreliable as a historical document, but it may contain little nuggets of historical information. The notice of Paul's citizenship may be one of these nuggets. One line of reasoning that lends it credibility is this: it is somewhat unorthodox to believe that the great St. Paul, hero of the early church and founder of much of its theology, was a legal citizen of the Roman empire, the very same earthly power that murdered Jesus. There is every reason in the world to leave it out. We know that the pious scribes who transmitted these document would often leave out material that they found embarrassing. The fact that they left it in suggests that Paul's citizenship, although embarrassing, was well known and widely accepted. Since they didn't have "plausible deniability," you might as well leave it in.
It is hardly unorthodox to believe that Paul was a Roman citizen. In fact, most Christians believe just that. In fact, it is the orthodox position, as in, it is the accepted position.
Also, if you notice in the Gospels, the Roman authorities are increasingly left off the hook. And later on, the Roman Empire embraces Christianity, and Christians still remember that. So the Roman Empire isn't this evil entity that people would want to make Paul unassociated with.
Now there really is no reason to leave such out. I have explained this earlier, but if Paul had mentioned it, it simply would have given him more credibility. That is why Acts does it. Obviously, it wasn't a problem some idea. And by Paul openly rejecting it, he would have appeared more humble. But even when Paul has an opportune time to mention such, he never does. Paul doesn't seem to be aware of such a status.
Finally, whether or not scribes left out material that was embarrassing really means little when we look at the NT, and see a lot of embarrassing material, some of which the Gospel writers actually go out of their way to try to explain.