From my understanding, Amazon doesn't currently make money off its Amazon Instant Video service.
Cheap, high quality streaming TV like this probably hurts (1) traditional TV channels, (2) online competitors like Netflix, and (3) any new companies trying to enter the online streaming market. On the other hand, consumers ought to be happy that their consumption is being subsidized (for now).
Is it fair to call this behavior "dumping"? At what point does "dumping" lead to anti-trust action by the government?
The US government, at least, basically doesn't enforce anti-trust regulations any more. And even if it did, the current administration's philosophy essentially doesn't include the enforcement of ANY regulations against businesses for the public good.