The TARDIS Traveller wrote:
Donna asked about that, to which 10 responded "Nah, Ancient Rome, anything goes!"
Which was absolute bullshit.
If he were presenting himself as a barbarian outsider, sure -- Romans were used to all sorts of odd costumes for foreigners. However he was claiming to be a government official, and the mark of a civilized man given that sort of responsibility is his willingness to embrace the cultural norms of the society -- to speak Latin with the proper accent (we can assume the TARDIS did that for him) and to dress like a civilized man.
I'll put it in modern terms -- in our society we're used to all sorts of outfits -- suits and ties, jeans and t-shirts, saris, Hari Krishnas in their saffron robes, Trekkies in Starfleet uniforms and pointy ears, what have you. If someone showed up in a Starfleet uniform and Spock ears claiming to be a government official, even if he had an ID badge that looked real to you as far as you could tell, wouldn't it weird you out? Wouldn't you be somewhat suspicious? That's the level of weirdness and suspicion the Doctor should
have been triggering, and his "anything goes" line was just ahistorical garbage to try to hand-wave it away.