It is worth noting we have discussed the illegality or not of detention centres already:
http://www.tfproject.org/tfp/showthread.php?t=68472
I think there is a need for somewhere to put people who have entered the country illegally or who have overstayed their visas. I don't whoever agree that people should be there indefinitely, nor do I agree that the conditions should be "prison-like". I advocate being able to process these people as quickly as possible and err on the side of accepting more refugees than less. I mean, it is not like we don't have the space for them...
And, if it is found that they don't have a case for entry into the country, then ship them from whence they came...
If the facilities were more humane, then compensation becomes a moot point.