Okonkwo, as much as he may be deemed a villian, was indeed a victim of colonization. Achebe's primary purpose, in my opinion, in writing Things Fall Apart was to highlight the evils of colonization.
Okonkwo was a leader of his people. Whether or not those who colonized his village believed he was morally right or wrong makes no difference -- the fact remains that the Igbo culture was debased and annhilated. Without the colonization of his village, Okonkwo would not have "fallen." He was a truly steadfast and stubborn man, but some would perhaps say he was the strongest for not giving in so easily to the newcomers.