[akavi]

Blame the person who chose to translate "petition principii" so terribly.

No one in isolation would interpret the Modern English phrase "begs the question" as meaning "assumes the desired conclusion as a premise"; the natural, "naive" interpretation is that it's synonymous with "raises the question". So why blame the reader for the translator's mistake?

If you need a translation of "petitio princippi", maybe you can use "assumes the conclusion" or "takes $premise for granted" instead?

[gweinberg]

I agree that "begs the question" is an awkward way of saying "assumes the conclusion", but it is also an awkward way of saying "raises the question". As the Mad Hatter sagely observed, one should say what one means.