Speaking as someone who has been underemployed for years, I can safely say that this advice is a load of crap. Yes, it is true that lashing out won't improve anything (although, there is at least the small chance that someone will listen to the lashing and change a policy, small though it may be). Also, the lashing only constitutes a poor attitude if it is both lashing and also wrong. In this case it looks like correct and well-placed lashing to me. It might not be rational to do it since it won't affect change, but it's not a "bad attitude" to do it either. Trying to label it as a "bad attitude" is, I believe, an alarming form of blame-the-victim mentality.
Underemployment can be an absolute career killer in technology. It can drain you of all energy to engage in personal tinkering or self-study to maintain current skills. Despite being intellectual drudgery, the work can still be emotionally and psychologically draining. It fosters burnout.
I'd rather see someone on the thread take a kind and caring attitude to a colleague here who is dealing with one of the really gruesome career problems of this field. Rather than some dumb finger-wagging about "just change your attitude."
The problem is so widespread & systematic, just like the open-office problem, closed/political allocation of projects problem, macho subordination/willingness to work in Agile/Scrum problem, and a host of others. It's like this because people don't lash out. No one stands up and protects their speciality ... many just embrace mediocrity and a steady pay check and figure who cares what the organization wants me to do. Then, if anyone should be so audacious and arrogant as to desire some bit of intellectual prosperity in life while still earning a living wage, they must have a bad attitude, right?
Many employers, especially large bureaucratic ones, actively look to underemploy people. They foolishly model that surplus labor as a latent benefit or an extra assurance that the baseline labor required of the position will be more easily guaranteed. There is almost no effort to model surplus labor as a source of burnout and turnover. Such things are swept under the rug of "bad attitude" or "not a team player" or whatever other subversive codeword that HR-types want to put on it.
Often they are willing to pay above market rates specifically to underemploy you. This is the double trap of not being able to build career-affirming skills on the job and also not being able to switch jobs without a pay cut.
It seems a lot of people just don't value intellectual prosperity most of the time. It works out for employers and the worker gets what they want and everyone is happy.
But if you are oriented internally, possibly at the genetic level, to be incapable of avoiding burnout and extreme, unsustainable job dissatisfaction when you are expected to be willfully underemployed, the system just can't handle you. There is no attitude adjustment that will fix it -- you could have the nicest and most polite disposition of all time, while suavely executing interviews and wooing management -- it won't matter.
Your unwillingness to be satisfied with underemployment is, in and of itself, considered toxic to bureaucracy. The bureaucracy system cannot function if intellectual prosperity is something it must actually provide for workers, rather than just merely paying lip service to it.
Anyway, I don't have any answers except to say that I totally understand where the lashing out is coming from. It's human. It's coming from an urge to call bullshit on underemployment and to vent frustrations about systematic mistreatment of underemployed workers. It doesn't speak to any attitude malfunction whatsoever, and labeling it as such is just one more of the many tactics that bureaucracy uses to expunge the so-called toxin. I can relate to this person. I feel compassion for them.