And if you save them, you also prevent the rise of any other dominant civilization on that planet, in favor of one that is fundamentally unsound. Is that your call to make? While you may willfully blind yourself to the ramifications of your decision, they still exist after you have trotted off feeling self-satisfied. Meanwhile, in 1000 years, the planet is still a barren rock. Still feeling generous?
That was one of the most ridiculous arguments ever presented in Star Trek. Sadly, the writers of that episode seemed so convinced that their "message" was intelligent and wonderful, so much that they performed a character assassination of the main character, who had been established as a guy who does rash and stupid things, but has his heart in the right place and an enthusiasm to help everyone. And then he acted out of character and decided not to help - and still for a very stupid reason. Well, I guess at least the stupidity was consistent.
Just how absurd is it to claim that you won't help someone because by saving them, you'd be playing God - when, by
refusing to save them, you've done just that? To make matters worse, you decide that they aren't worth saving, because, oh shucks, that might, possibly, or not, sometime in the future, prevent another species from taking over!

Gotta help the other species take over. Wait - how the hell is
that your call to make?
No, better off to refuse to help, even though you can, and trot off feeling self-satisfied, because you were so wonderfully smart and long-sighted, that you refused to save people because of what might or might not happen in 500 or 1000 years! Nevermind that you actually don't have a fucking clue what will happen in 1000 years, and you're just making a lot of assumptions - say, that the existence of one species will hurt another - even though the other species has been developing while living alongside the first one - or that two civilizations will be incompatible. How the hell would you know that?! You have no proof of what is going to happen in 500 years. In making all those assumptions and basing your decision on hypothetical future scenarios, you're, in fact, playing God.
What was certain - not just an assumption - is that people were dying, in the present, and they had the means to help. Helping save lives, if you can, is not "playing God". It's what civilized humans are expected to do. And it's what ever medical doctor or medic does that whenever he/she treats someone. It's what their profession is all about. If giving people cures that they did not invent themselves is "playing God" and averting the course of nature, well, why don't we just abolish the medical profession?
You can not save everybody in the universe, nor should you feel it's your obligation to do so. Same as here in real life.... people suffer, people die..... not everybody is supposed to live a long life..... not everybody is going to have a 100% joyful life.
So, I bet you think that, when you see a person drowning, you should never try to save them? When you see a person on the street getting raped or beaten to death, you should just walk away and ignore the whole thing? Meh, it's none of your business. They should fend for themselves, if they can't, they were not strong enough and they should die. If you help one person, next they'll be expecting you to save everyone! Can't have that!
They will progress and develop based around federation/starfleet teachings, technology and history, and chances are, abandon many of the things they once believed or developed to adopt the easier path of tacking technology and information already created for their own.
Be given a car or build it yourself?
Sure, being given a car is quick and easy and you'll know how to use it..... but if you take the time and effort to build it yourself, you not only know how to use it, you know how it was built, how it works and be able to fix it yourself when you need to..... not to mention improve and evolve it a lot easier.
Yeah, I bet every driver you see on the street has built their own car.
It's pretty stupid having to invent things that have already been invented. I don't see the necessity of living in 18th century conditions before I personally manage to invent electricity - since someone else has already done it long time ago.
If you're going to try to invent new technologies, it makes a lot more sense if you first know what technologies already exist. Then, instead of treading old ground, you can actually contribute something new. That would certainly help progress a lot more than 1000 different people having to invent things that have already been invented by others.
There are such things as sharing knowledge and cultural exchange. I don't see European cultures being hurt by the legacy of the Arab medicine, which was superior to the European during the Middle Ages.
Take a look at our own planet as an example. How many times have we in the past asked help from aliens to solve our problems.... better yet..... when was the last time you can remember God or Gods coming down to help us in our time of need(s) when we asked for it?
