And if you are walking in to the court for a hearing on your asylum claim, that provides probable cause that you are an illegal. Open and shut, except for not having "legal due process" before you are deported to El Salvador. Not being a law major, there is something I am not grasping about how punishment can be imposed, with "legal due process" completely denied.

They can't deport you without a hearing (certain exceptions not relevant here). They can detain you without a warrant.

So if you're walking into court for a hearing, they can take you into custody. If you have been detained wrongfully, you have the ability to request after-the-fact relief from being detained, if your detention was not lawful (just like you have a right to an arraignment and bond hearing and habeus corpus in the criminal arena). But you won't be given that hearing unless you are at least alleging that you have some right to be free from detention. And many (most) folks who are being detained simply don't. Just because ICE has previously let you walk around free during the pendency of your final hearing on your immigration status, that doesn't mean they don't have the legal right to change that and detain you.