Why Was the Book of Revelation Written Symbolically?

A common view among Christians generally is that John wrote the Book of Revelation in symbols as a kind of code. The church was experiencing persecution and John wanted to write critically of Rome in such a way that the recipients of his book would not get in trouble for harboring such an inflammatory document. He wrote in symbols so that any non-initiated Roman would fail to understand what he was reading, and thus the church would be spared further persecution.

I taught a class on Revelation tonight in a church, and this idea came up. The idea itself is wrong, and I said so during class. But following class I reflected on the idea a little more and eventually determined five reasons against it. I thought I would list them here.

1. There is no evidence that the Romans attempted to censor Christian literature in this way. 
2. It would take a pretty ignorant Roman censor to fail to notice that the harlot riding the beast in ch. 17--the beast with seven heads which are seven mountains (17:9), and the harlot that is the great city (17:18)--represents Rome. 
3. Christians did not shrink from directly challenging Roman authority, by doing exactly what John wanted them to do: refusing to participate in Roman religion. This often resulted in martyrdom for Christians, which they welcomed; they did not flee from it. Moreover, Christians knew how to directly insult the powers-that-be in their literature.
4. Revelation is written in symbols because it is apocalyptic literature. That is how apocalyptic literature works, and there are plenty of other examples to bear out this point. If Revelation were the only example of this type of literature, then we might have to devise an explanation for all the symbols, but it is, in fact, not unique in this aspect. And it would be foolish to argue that all apocalypses were written as such in order to avoid punishment for their readers. 
5. The symbols are essential to the message that Revelation wants to convey. It is not as if John wanted to communicate a message to the churches and then decided to do so symbolically. No; the symbols are integral to the message. John wants to reform our minds, to transform the way we see reality. He cannot accomplish this 'conversion of the imagination' (to borrow a phrase from Richard Hays) without the powerful and unrelenting symbols. 

Those are the arguments that popped into my head. Of course, none of these are original with me, but I thought it would be helpful--to me, more than anyone--to gather these thoughts in one place. Let me know if you have more to add to the list.