Comey either knows what additional effect a backdoor in encryption will have (in addition to providing him access) or he doesn't.

If he does then he's either a traitor or an idiot and not capable of fulfilling his role, and if he doesn't then he's an idiot and not capable of fulfilling his role.

This is his strike 3, after the iPhone debacle where even the NSA told him to stop being an idiot and the Clinton email investigation.

2/3rds of crypto is non-US made ( https://www.schneier.com/paper-worldwide.html ) so this backdoor will only affect US citizens/companies and only they will be vulnerable to it, it'll decimate the industry there.