Okay, I'll ask again. Based on the misleading article you posted, how is the union defending him? 
By urging people to use "skepticism and caution," which is precisely what the AA employee did not use.
Look at the lady on the video posted on another thread (an image is worth a thousand words). Look at how the person who hit the lady is acting. Is he sporting a conciliatory and calming attitude toward the lady (who is holding a baby and seems like about to have a breakdown mind you)? Does he look like a person who has done nothing wrong and wants nothing but to appease a distraught person and her baby? NO, in fact, what YOU and I see is a jerk off in full hostile mode. Even the flight captain has to intercede so that the situation does not escalate.
Has American Airlines apologized for the incident? Yes. Why? Because, as the video shows, the flight attendant's attitude is extremely damaging, showing NO concern whatsoever for the distraught party.
So, to re-re-reiterate, with all the evidence at hand, and American Airlines' apology on the table (something they no doubt did because, after the other employees were interviewed, they can smell a large lawsuit on the way,) why would the union come out and issue the usual generic call for "caution" and to wait for the internal investigation to end? To show what? That hothead Joe had too many shots prior to getting on the plain and the darn lady would not let go of the stroller?
Not only that, the fact that the union included the other passenger in the
communiqué makes the whole ordeal the more surreal. This was done with very ill intentions so as to obfuscate both events into some sort of larger altercation from which the AA employee was equally ill-treated. Bullshit. The fact is that the passenger's last outburst was nothing but a RE-action to the AA employee's hostile attitude.