2001: A Space Odyssey ~ argument 

This potted argument will probably not change your mind. If you are set against the interpretation from the outset, you will be able to dismiss most of it. If, on the other hand, you agree with it, then you’ve probably already experienced mushrooms. The points are made quite summarily here, for those wanting to dig deeper I recommend following up on some of the references (e.g. reading Terence McKenna's "Food of the Gods").

The Obelisk is a Metaphor

Most will agree that the remarkable film '2001: A Space Odyssey' has a strong psychedelic aspect. However, while this is most apparent in the final scenes, the more wholly it is taken into account the more integrated the rest of the film becomes (that is, it's not simply a tacked on hippy-enchanted ending).

The likes of Gordon Wasson, Terence McKenna and others have brought attention to the fact that naturally occurring plant psychedelics, in particular mushrooms, have been used since prehistoric times. In fact, historically speaking, modern society's taboos and fears about these substances are a relatively recent anachronism.

More so, it can be seen that if the use of mushrooms and the like goes back far enough it can be argued that these substances could have played a significant role in the development of human consciousness, acting as a kind of evolutionary springboard.  On investigation one will find that naturally occurring psychedelics have played a key role in the development of human consciousness. For example, they are found in the origins of practically all religion

Somehow, humankind lost touch. Over time their use became unacceptable to the ruling orthodoxy, - people are difficult to control if they will not simply believe what you tell them. Maybe to an extent the mushroom itself withdrew, temporarily. On a different time scale, if you consider where we are now, and as suggested in the films extraordinary transitional scene from the dawn of man to the space age, it has been no more than the historical blink of an eye.

Anyhow, the plants' secrets did not die out; instead practitioners learned to make only cryptic references for fear of persecution. This practice of cryptic reference has perpetuated and is echoed in the film, - regardless of whether Stanley Kubrick or Arthur C Clarke consciously intended it or not.

And so for what is the obelisk a metaphor?

Behind the black block you will find the censored mushroom.

Modern day psilocybernauts will confirm how the mushroom can propel you through a hyperspace vortex into a transcendent realm (beyond time), ...sound familiar?

There is more that could be expounded. The sense of another evolutionary leap (to Star Child), but, at this stage, you have either gone, ahh! or you have gone, huh?