One of the many arguments being used here is that it's the city's decision to become a sanctuary city, which is completely true. Any city can decide to be in defiance of federal law whenever it wants, they just won't be funded by those who put the laws in place to break them. Federal funding isn't a city's "right", it's the reward for upholding federal regulations and laws, and should be thus used for the purpose of doing such, instead of drastically and illegally opposing the federal laws that give them those very funds. This isn't true only for this situation either, federal funding should be cut from any state or city that defies federal laws of any kind. If you want something to become legal, make it legal before doing it through due process, otherwise the system will punish you for it.