Dark matter is an explanation for why galaxies spin much faster than our model for gravity permits by given the galactic mass their stellar population implies. For dark matter not to exist, our model for gravity and/or our model for stellar mass has to be wrong.
Dark energy is simply a plug label for whatever is causing the well-observed accelerating expansion of the universe. The only way it doesn’t exist is if those observations of expansion are wrong.
Replace Unicorn matter for dark matter and Unicorn energy for dark energy and your post still works.
;-)