Decriminalizing something should be done by changing laws. We would not say that the Southern states prior to Civil Rights legislation had decriminalized white men murdering black men, we would say that those Southern states were violating their public trust by not enforcing the law.
The law is not some words on a page; but a system of interacting interpretations and social norms. The public trust violation isn't that a bureaucratic/executive method of law-change allowed for lycnhing, in that any law-change allowed for a group to be terrorized.
Our founding was on the back of the British breaking this same trust by not protecting us during the french-Indian war; a similar violation of trust.
No, immigration law being changed does not murder anyone; and while those that have a deep-seated xenophobia may not want to be around brown people that speak Spanish, this is hardly a violation of the public duty to protect life, liberty, and property. Instead it is a markets issue.
There is a market for their labor, if there was not then they would mostly go home. Since there is demand for the labor they supply and the labor they supply is illegal, they are part of the black market (much in the same way a drug dealer is). But in the case of decriminalized labor-delivery, that black-market labor becomes much more 'grey' or simply 'informal' instead of 'renegade'; in exactly the same way as the decriminalized pot-bar is part of an 'gray' market, despite violating the letter of the law.