We traditionalists prefer to adhere to the original (Greek) * -ize* spelling, and not join the trendy, Gadarene with their affected (French) -ise spelling.
Here is the OED on the subject:
Concerning the suffix itself, whatever the element to which it is added, is in its origin the Gr. -ιζειν, L. -izāre; and, as the pronunciation is also with z, there is no reason why in English the special French spelling should be followed, in opposition to that which is at once etymological and phonetic.
In this Dictionary the termination is uniformly written -ize.
It is clear that it has always been "accepted practice" in British English to spell such words as -ize, and
if there is any "pedantic" argument to be made, it would be one that accords with the OED and that would say that to spell the words in the French style as -ise should not really be considered correct even in British English!
(Various sources)