If somebody goes beyond fourth jhanas and has received super knowledge and also powers, than why don't he shows it to world and shares his knowledge and experience to world or say scientist and science community so that the general humans will believe in dharma and religion?
If the story of Jesus is believed to be true, Jesus did what is suggested in the question and look how Christianity turned out; thousands of years of killing over a (narcissistic) personal saviour.
Acts of magic or witchcraft will not change the majority of people for the better. This is why DN 11 teaches with proper wisdom the 'miracle of instruction' is superior to the 'miracle of psychic power'.
The objective of Dhamma is the work yourself out of stress and misery which is to follow the Noble 8 Fold Path. These kinds of practices diverts from this focus. If someone start practicing being attached by such display then most likely their goal will not be tied with the Buddhist goal.
Perhaps for this reason monks are not supposed to display such abilities. Even for lay, through there is not rule, it is not advisable as you are diverting the attention and focus from the true purpose of the practice. Also then meditation practitioners will be no different from magicians and illusionist, like David Copperfield. People will go to them to learn magic tricks and not to learn the dhamma with a view to Nirvana. People go to see David Copperfield for entertainment and not spiritual guidance! Also when displaying these abilities one might develop pride which would lead to one's downfall.
Displaying these abilities may attract a following and belief, but for the wrong reason.
Kevatta (Kevaddha) Sutta: To Kevatta
This Sutta talks about the drawbacks of displaying magical powers.
tl;dr it mostly just does not prove anything other that you do have the powers, people will still try to argue that it is not what you say it is.
Of Leonardo da Vinci it is known that he invented the principle of submarine boats - but also it is transmitted that he explains "why I do not give this to the open: because they would use it for even more warfare on the sea" (paraphrased from memory). Similar caveats have been sometimes explicated in science (for instance with atombomb by Einstein and others - documented in a biography I've read).
Anyway... the best answer on this has surely been given by @Suminda and the idea with it should be a frequent topic in self-observation and meditation.