There seems to be a lot of confusion about the gatekeeping criteria for first contact and Starfleet's Prime Directive. Allowing contact only when a species develops warp drive is not about them achieving some threshold of maturity or technological sophistication that would mean they are somehow "ready" to be contacted and deal with the reality of living in a galaxy full of starfaring alien civilizations.
The reason that achieving warp drive is the checkpoint for contact is that there's no longer any way to avoid it. As soon as a species gets warp drive, they will be out among the stars and will soon encounter alien civilizations. There's no point in trying to keep them isolated when they can just fly to another star and meet aliens there.
So, in my interpretation, the first contact rule is entirely pragmatic, and not based on whether a civilization is "ready" for contact. When it's obvious contact will happen one way or another, that's when you should step in and do it under controlled circumstances.
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