That doesn't mean you don't have due process to establish that the individual was actually undocumented. You don't skip due process. What's so hard about that? What if the individual is actually in the country with all of the correct paperwork and visas?. That's what you figure out via due process before acting.
Non-citizen residents in the US are required to carry proof of immigration status with them at all times, precisely because of this scenario. Immigration officers/enforcement, in basically every country, have a substantial degree of independent discretion.
