The term manic depression at least mentions what these "poles" are, whereas bipolar could easily be interpreted by the uninformed to mean a mixture of really awkwardly icey and outrageously rude and poorly disciplined.

Of course I am assuming that the general population has a vague clue what mania is, and perhaps that is the problem with the term manic depression. "Mania sounds like maniac. Hmmmm. Surely a maniac is a deplorable, badly behaved person you would never want on your list of contacts, let alone be seen hanging out with them. Keep away from my children, pervert!!!"(sarcasm)

When someone has known me only during a euthymic phase, they don't seem to get it when I mention that I struggle with bipolar disorder, that sometimes I get clinically depressed. Maybe it is just the influence of the media drawing attention to cases of deliciously bad behaviour to report on, and little mention is made of the pain bipolar sufferers are in.

So both labels have their problems for me.
Even the diagnostic criteria are really just part of a man made construct and are describing only a fraction of what is really going on in each of us. Symptom overlaps, false dichotomies, arbitrary cut-offs between levels of severity, poorly understood mechanisms and causality, etc. are all evidence of how shaky and transient our "disorder" labels and criteria are.

I'm not happy with the diagnostic labels, but they do give us something to identify with and hopefully get some form of a grip on the chaos to get our lives into a manageable and productive state.