Yes, sikhism do believe in forgiveness. But to whom, the person making mockery of your religion or your gurus or even killed your people after that. then also, forgiveness can be granted, but the person seeking forgiveness, has to ask for. Not make fun of forgiveness.
Can india forgive Pakistan? Even after so many attacks happening daily, can we stay friendly? We are friendly, but only civilians and to some extent politicians too? but what about solidiers who are laying off their lives, can their family members forgive jihadis??