> Given all this history, to me it is utterly bizarre that Trudeau cares to defend this dubious group of alleged terrorists more than maintaining diplomatic and economic ties with India

Setting aside the morality of who is right or wrong: my understanding is that just like in the USA, domestic politics are far more important to Canadian politicians than geopolitical concerns. Trudeau likely feels that he and his political coalition cannot afford to alienate Khalistani supporters - if they do so, then they will lose political power until a new coalition can be formed.