There is no career for most PhD students. This is the whole problem with how people look at it. If it were the case that most people with PhDs could obtain stable, low-paying academic jobs, then you'd have a point, but most people with PhDs can't do that.
I agree with you that counting on a stable job in academia is probably a mistake for most PhD students. But your previous categorical statement goes too far.
It's a perfectly valid choice for me to decide to do a PhD for no reason other than an intense desire to learn more about some topic and then plan on making a living as a kayaking instructor or elementary school teacher or a handyman for the following two or three decades. As long as I have no delusions about the feasibility of my plan.
Of course, if you want. But surely it's unwise to actively encourage someone along that path. If it's what they really really want, they'll do it anyway. Advice is directed at people who are undecided.