At one level, it's very simple. A person employed in a public relations role has a professional duty to defend their employer or client.
But it's more complicated than that. Questions of personal conscience might intrude (and some of these aren't as simple as saying that non-smokers should avoid representing big tobacco, or vegetarians should avoid working for a meat packing business). Then there's the question of the public good (which should override personal or organisational interests).
There are legal issues too. Positive PR spin that might have encouraged people to invest their savings in a failing (or fraudulent) business could lead to 'class action' style lawsuits. That you acted 'in good faith' is not good enough.
I'm sure there's more to this case, but on the face of it a Ministry of Defence press officer is claiming that defending his employer over the many recent deaths of soldiers in Afghanistan caused him severe stress.
Sometimes it seems that we're damned when people consider the PR function to be trivial (puffery) and we're damned when we take personal responsibiity for the language we use and the effect it can have (even in matters of life and death). Can this really have been a case of 'careless talk cost[ing] lives'?