From the other angle, targeting their competition's employees could also be seen as immoral as well. Say google used their big money for a year or two and literally threw money at someone like amazon's engineers, offering them like 1 million a year each? Not even if they needed them, but just so that amazon didn't have them anymore? Amazon would be out of buisness if they couldn't maintain and improve their services. That is anti-competitive and monopolizing in it's truest form. This act of mutual assured destruction is being spun as anti-competitive as well, but I just can't see it truly being that way.
Refusing to hire one company's current or previous employees is one thing, but agreeing to not actively head-hunt each other? That's where the breakdown is at.
The price fixing part is the strongest argument, but I personally see it as a sanity check. If google or apple *artificially* made the career field for software engineers go from a national average of 100-200k a year to something like 400-500k a year no software company startup (or even those just not as successful) would not even have a chance to compete. That ultimately boils down to a problem with the free market though, if that really could be seen as a problem at all, but at some point I feel it could be abused and turned into monopolizing the market. Like I said, questionable morality at best.
Now if the price fixing was at the lower end of the compensation tables like them all getting together to keep a highly skilled job at a minimum wage to boost profits, that's evil. (outsourcing to india *cough cough*) But keeping the price at a national average and appropriate for the actual demand for that type of worker, allowing for just compensation for the skills required, that in my opinion, is just sanity. If there was a true lack of personnel in that field and the price goes up, fine, but at the level and subject matter this article is talking about is directly in line with scouting each other's employees in terms of stopping each other from creating a monopoly by uprooting the gears that make those other companies work.