Rejecting God's commands is rejecting God. #faith in YHWH inevitably leads to obedience, while disobedience shows lack of faith.

Israel's assault on Amalek was the same as Nadab and Abihu's strange fire. Disobedience = Disobedience. The people are collectively guilty if they collectively sinned, regardless of individual innocence. It doesn't matter if we think God's judgments and instructions are fair or not. We might as well curse the sun for being too hot. It is what it is. Deal with it.

See Numbers 14-15.