There are different issues to consider here.
Was the flight attendant within his rights, or was he even smart, to have sex in the airplane's bathroom while wearing his uniform and name tag?
I would say no, as a representative of the company, his behavior was inappropriate and the airline was not wrong to fire him.
If he DID know that he was being filmed, should he have let the recording continue? Again, I would say no. That would have been a truly unwise decision, and he would have knowingly been putting himself and his future employment at risk.
BUT! If it is true, as he says, that he did not know he was being recorded, and AW filmed their private sexual encounter and then uploaded it to the internet without the flight attendant's knowledge or consent, that is egregious; unethical and reckless at best on AW's part, and criminal at worst.
The FA might indeed have let his little head override his common sense. He may have made a really bad decision to engage sex with a stranger in the bathroom. (Who here can cast the first stone, LOL?) I still believe, however, that being dumb when offered the chance of hot sex does NOT justify AW's taking away the FA's right to choose whether or not he wanted a private sex tape shared with the world. That was unwanted, damaging exposure and a smarmy violation of the FA's private life. AW was totally in the wrong and the employee did not deserve such vile behavior.