"...Why should tax payers pay for the miscalculations of others ?..."
Because the government chose to change the rules without any forewarning, so they (the government) should be responsible for their own actions.
If the government tried to do otherwise, they would most likely lose any court challenge, as it wouldn't meet any ethical or moral standard, let alone any common law standard.
The government are doing the right thing by paying the cost of the incarceration of returned travelers.
If the government chose to warn travelers before they left that they would be up for the cost, then that would be fair enough.
