Diabolically opposed

Diabolically opposed is frequently used, meaning at least two ideas are in extreme opposition. Why "diabolically," as in devilishly or fiendishly?

Do you mean diametrically opposed?

Google gives 623 instances of "diabolically opposed", so the quote is right. I take it it's a humorous expression, and the fact that one can hear "diametrically opposed" within it, only adds to the fun. On the other hand, it's sound kind of Miltonic: Better to reign in Hell than serve in Heaven. Thus spake the Apostate with fiendish wrath, diabolically opposed...