It is not a crime to repair a vehicle and as long as you are still compliant with your state's emissions laws (most are much less strict than what an EPA/CARB requires for a 50-state vehicle) then there's no issue.
I think the EPA would disagree. EPA rules still apply to vehicle owners even when the state laws don't duplicate the EPA regs. The only time you can be in compliance installing an aftermarket component in an emissions system is "when an individual or company has a “reasonable basis” to believe their actions do not increase emissions." The secondary air delete kits pretty obviously fail to meet this. The only compliant repair is to get the system working again.
There are many people and fleets that have been successfully prosecuted for violating EPA regs, with no regard for what might have been legally enforced in their home state. EPA supersedes the state's rules.
Also interesting:
Q2: Am I protected from selling a defeat device or tampering as long as I inform my customers that they can only use my parts
“off-road” or “for racing use only” or that the parts are “not for installation on emission-controlled vehicles”?
A: No, if the parts are designed for and intended to be installed on motor vehicles, EPA considers you to still be liable under the CAA prohibited acts. The use of the motor vehicle is irrelevant.
Simple little legalese language doesn't protect sellers of the defeat devices. They just need to hope the EPA doesn't decide they're worth prosecuting.
The fortunate part for most individuals choosing to delete/modifying stuff is that you're at a very low risk of actually facing any penalties. Similar to failing to disclose income to the IRS, your chances of getting caught are very low. If you are caught and prosecuted, though, the penalties can be severe.
Don't mean to be preachy on this stuff as I have a few non-compliant setups for my Supra, but I don't want people being led into a false sense of security.