I think there is this discussion because sometimes Government Rates are cheaper than the Best Available Rate or any other rate. People should stop getting upset if government workers sometimes gets lower rates. I think there would be similar outrage if government workers keep booking more expensive government rates even if cheaper rates are available.
Morals are moderately different from one place to another depends on country and culture. Using your corporate rate/government rate for non-offiical business is one of those very personal choice. I consider it the same moral standing as using your personal relations with the manager of the hotel to get a lower rate for your work travel or co-worker's stay than you otherwise would get under normal conditions or using your personal AAA/CAA status to get a cheaper rate for work-related travel.
In this age, I don't think there is 100% vacation. People sometimes read their work email or even have an urge to respond to them during vacation (this is still work related). So if the lines between work and vacation starts to blur, using your corporate rate for personal use or using your personal rate for corporate use is also getting blured.