In Star Trek, the Prime Directive was the constant looming moral law that starship captains had to constantly bend to the breaking point to do what was right. I understood the premise and even could see where I largely would agree in such a law, but it strikes me as being so unfeasible and unreasonable. It's no secret that the Galactic Concord in Mythic Space is tailored after the Federation, and I've even mentioned a Prime Directive like edict in this post about the Galactic Concord. I modified the benchmark to something that I felt more befitting of a sentient species, but even then I suspect there would be plenty of contacted and exploited primitives in the galaxy.
The Concord set the benchmark of being able to send satellites and probes into orbit and beyond as the point at which contact with a new species can begin to be established. There is a large set of guidelines that require reconnaissance of the species' culture, history, religious beliefs, and so forth that must be passed before first contact can be initiated. That's all well and good, but there are plenty of stellar nations and organizations in the galaxy that don't give a damn about letting a primitive species evolve culturally or even biologically without outside influence. They see profit either in the form of slaves, easily attained natural resources, or both. Therefore, while the First Contact Edict is strictly followed (largely), leeway and captain's discretion have became much larger factors behind how stringently the First Contact Edict is adhered to. After all, a starship captain trying to keep his crew alive and make repairs to a crashed ship isn't going to really care about hiding knowledge about life among the stars from a planet's primitive residents.
The First Contact Edict was put in place largely for two reasons. The first is the idea that species should be allowed evolve both biologically and socially without outside influence. Detractors to this point argue that there are many instances among Concord members where outside influence shaped them into the species that they are today. Then there is the argument (used both for expanding the application of the First Contact Edict and for abolishing it entirely) that the First Contact Edict should apply to all species. No one truly knows what species in an ecosystem will achieve sapience, if any, so even on a world with no sentient life at that moment may be irreparably changed by contact with outsiders.
The second reason is that not all species are able to properly cope with being exposed to being part of a galactic community. A variety of factors play into a society being able to fit into the grander cosmic neighborhood from religion, socio-economic factors, to governing systems. Some species see alien visitors as demons or angry spirits that either need to be defeated or appeased in some way. This can lead to mass sacrifices or literal witch-hunts with the first contact Ambassadors being the witches, neither option is desirable. Governments that keep their populaces governed with fear of the unknown are just as dangerous to first contact Ambassadors, as they often see aliens as a threat to their power base and will likely shoot first and make up the "facts" later. Then there are the species that are simply unable to parse being part of a world so much more advanced than their own. Arthur C. Clarke once wrote that "Any sufficiently advanced technology is indistinguishable from magic." To those from primitive worlds seeing starships, laser rifles, computer systems, holograms, not to mention the massive variety of strange and even sometimes monstrous forms of life they feel like they are know in a world of nightmares. Even those that are able to understand that a Weren is just another being trying to survive, may not have brains evolved enough to understand how to use all of this technology. Where do those beings go now? How can they possibly fit into cosmic society when they can barely operate the front door? However, there have been very few instances where a species is willing, but simply unable to join galactic society. It may take time, but in the case of two of the most primitive species to be ushered into the Concord far too early, Ewoks and Betaurians, both have been able to make strides into being full-fledged members of the Concord...even if most of their species still prefer to live according to their traditions.
Initially, the punishment for Concord captains, both civil and government, was severe. Hefty fines, incarceration, and possibly even the loss of their ships/commission were possible. Today, the punishments stand, but the application of the punitive damages are up to judge in each case based on the circumstances surrounding why the First Contact Edict was broken. In cases of down starships, it is considered ridiculous to adhere to the Edict in lieu of focusing on survival. However, taking advantage of a primitive culture to essentially steal valuable resources will see a captain, and most of his senior crew, sent to The Clink (nickname for Jarnbash Orbital Penitentiary, one of the toughest prisons in Concord Space) for a long time.
Just because the First Contact Edict isn't as rigidly applied today doesn't mean that there are no programs in place to try and help ease "primitive" cultures into being part of a wider community. The Concord's Office of Xenological Research has a First Contact Bureau that handles cases where the First Contact Edict has been broken and the species exposed to the realities of the cosmos essentially can't go back to life before for whatever reason. They attempt to find ways to gently bring in these species into the galactic community. Most of the time, primitive cultures exposed to advanced and alien technology simply create new legends to "write off" the experience in their history.