how they had gone about it , was not to be specified ; nor their motives , until at last gambier added , in an ironical tone , `` and of course , it is the slave trade to which they objected so violently ; although as everyone knows , the natives of the continent have made a practice of it from time immemorial , long preceding the arrival of europeans on their shore ; or perhaps i should say , of course it is they , who objected to the trade .