According to Wikipedia. The Non Interfere Policy is written like this :
As the right of each sentient species to live in accordance with its normal cultural evolution is considered sacred, no Star Fleet personnel may interfere with the normal and healthy development of alien life and culture. Such interference includes introducing superior knowledge, strength, or technology to a world whose society is incapable of handling such advantages wisely. Star Fleet personnel may not violate this Prime Directive, even to save their lives and/or their ship, unless they are acting to right an earlier violation or an accidental contamination of said culture. This directive takes precedence over any and all other considerations, and carries with it the highest moral obligation.
But guys, not to mention that it is too idealistic, but also, is illogical. Because space is not belong solely to the United Federation of Planet. There are Ferengi, Klingon, Romulan etc who can interact with these people, even when The Federation / Star Fleet not. So what's the point then? Does Federation capable to protect those "Medieval Era" Species from other Great Power? They are not the sole Super Power who can tell every one to do their biding. And Star Fleet won't have enough resource / military capability to protect all the lesser technologically species from Romulan, Klingon, Dominion, Borg, etc.
Plus, the reason that those creature will polluted by the 24th Technology is sound stupid. If they are not ready to learn the 24th Century Technology, then they won't be able to learn it even when you teach them how to build Warp Drive.
So, I think, it is stupid, and pointless.
As the right of each sentient species to live in accordance with its normal cultural evolution is considered sacred, no Star Fleet personnel may interfere with the normal and healthy development of alien life and culture. Such interference includes introducing superior knowledge, strength, or technology to a world whose society is incapable of handling such advantages wisely. Star Fleet personnel may not violate this Prime Directive, even to save their lives and/or their ship, unless they are acting to right an earlier violation or an accidental contamination of said culture. This directive takes precedence over any and all other considerations, and carries with it the highest moral obligation.
But guys, not to mention that it is too idealistic, but also, is illogical. Because space is not belong solely to the United Federation of Planet. There are Ferengi, Klingon, Romulan etc who can interact with these people, even when The Federation / Star Fleet not. So what's the point then? Does Federation capable to protect those "Medieval Era" Species from other Great Power? They are not the sole Super Power who can tell every one to do their biding. And Star Fleet won't have enough resource / military capability to protect all the lesser technologically species from Romulan, Klingon, Dominion, Borg, etc.
Plus, the reason that those creature will polluted by the 24th Technology is sound stupid. If they are not ready to learn the 24th Century Technology, then they won't be able to learn it even when you teach them how to build Warp Drive.
So, I think, it is stupid, and pointless.