This is not true. Teleology is one of the most controversial concepts in biology and many are very scared of it. I was trying to target those with these deep seated fears when asking those rhetorical questions.
What about replacing the cockatoo with a person (and bin -> can):
modified quote > "Can it really be scientifically justified though to say that a person has the 'goal' of opening the can to get at the food inside? Or are we relying on person consciousness or invoking some kind of weird causality here?"
The problem with teleology is when it's used to explain why thing evolved, for example that frogs evolved legs to walk outside water. It's not a problem when it's used to explain that the frog eat the fly because it was hungry.
It's irrelevant to the argument, because growing roots isn't learned behaviour.
Edit: I feel like I can expand even more on this. Plants grow roots to get water is a simplification, roots can serve a lot of purposes. Roots can anchor you so wind doesn't blow you away, and it helps you to extract other nutrients from the ground with their high surface area.
It's entirely possible for evolution to cause something like roots to form in an organism because it helps one of these purposes, only for it to become useful for another purpose some time later.
The ability for roots to extract water from the ground does not mean that roots were evolved for this specific purpose. Case in point: many kinds of algae have roots and they are literally soaked in water at all times.
It is not unreasonable, at least in ordinary usage, to say “plants grow roots to get water.” Note, however, that your original phrasing was "a plant wants to grow its roots to find water."
In the context of your article, the use of "wants" here invokes, tacitly, the concept of agency. Furthermore, this is done as the coda to a section in which you discuss cockatoos learning to open garbage cans from one another. There's no problem, in the case of humans dumpster-diving, saying that they want to find food (or evidence or secrets, depending on the case.) It is a bit of a stretch, but not much, to suppose that the cockatoo behavior is driven by wanting to find food (especially, if, as you suggest, they are acting on a mental model of garbage cans as good food sources.) In the context you had set up, introducing "wants" into the quoted phrase question-beggingly prompts the unprepared reader to tacitly accept the not-explicitly-stated notion that plants want to get water just like cockatoos want to get food.
Perhaps you are thinking that there is a little bit of agency in what plants do, similarly to how some people will say (and have said to me - I'm not making this up) that a building with a thermostat is a little bit conscious. The problem with this sort of claim is not that it is provably wrong, but that it is practically useless, as the differences, between how a building regulates its temperature or a plant gets water on the one hand, and, on the other, how humans - or cockatoos - act on the basis of learning from one another, are so great that trying to discuss and analyze one in terms of the other leads to confusion rather than knowledge. If things reach this point, it has become a discussion of English-language semantics rather than anything about the natural world.
This is not true. Teleology is one of the most controversial concepts in biology and many are very scared of it. I was trying to target those with these deep seated fears when asking those rhetorical questions.
https://plato.stanford.edu/entries/teleology-biology/