Finucane wrote It's an expletive widely used in the British Isles which in polite society was once considered as taboo as "fuck."  Eric Partridge in his A DICTIONARY OF SLANG AND UNCONVENTIONAL ENGLISH assiduously avoids any etymology, but he notes that its use became much more acceptable in polite society after World War I.  Farmer & Henley, SLANG AND ITS ANALOGUES (1890) wrote, "An epithet difficult to define, and used in a multitude of vague and varying senses.  Most frequently, however, as it falls with wearisome reiteration every two or three seconds from the mouths of London toughs of the lowest type, no special meaning, much less a sanguinary one, can be attached to its use."  They think it derives from the word "bloods," which described "aristocratic rowdies" that raised hell in London during the 17th & 18th centuries.  They don't think it comes from the curse, "God's blood" or "'sblood!" that was common in Shakespeare's day.  My own feeling is that language being as plastic as it is, the older expression may well have contributed to or reinforced the later meaning and usage.  The earliest citation of "bloody" in the modern sense in F&H dates from 1676 but they note that in their day (mid-1800s) the word "blutig" was common among the people of Dresden as in "Ich hab keinen blutigen Heller mehr," or "I don't have a bloody cent!"  They note a similar usage in both France and Holland.

Wow......I'm speechless...you really did your research on that one.  Well done good sir, I enjoyed my history lesson for the day.