Complex sentence: Biko and his comrades regarded multi-racial anti-apartheid groups as unwittingly replicating the structure of apartheid because they contained white individuals in dominant positions of control, and so did not participate in these multi-racial organisations.
Split into simpler sentences: Biko and his comrades regarded multi-racial anti-apartheid groups as unwittingly replicating the structure of apartheid because they contained white individuals in dominant positions of control. For this reason, Biko and the others did not participate in these multi-racial organisations.