The problem is that customs officials (and immigration officers) are granted an extreme amount of power through discretionary authority. Congress has yet to act

The problem is that customs officials (and immigration officers) are granted an extreme amount of power through discretionary authority. Congress has yet to actually constrain this, and from my understanding the statutory language is so broad that determinations can be made based on literally anything. Which is why that hole "abolish ICE" got quite popular (and in many places is still around). Congress and the courts are way too deferential when it comes to these two, instead of holding them up to an incredibly high standard and giving the courts that level of discretion, which is where it belongs.