[Kuruharan]

But to attempt to keep a people confined forever, even if it is for their own safety, is simply doomed to failure as those people will want out at some point.

This does not release the protectors from their duty to try.

people do not always follow rules

Clearly there should never be any rules of any sort because somebody at some point is going to break them.

When Eol comes to Gondolin he will not allow him the possibility of leaving.

Because he'd already seen that bad things came of letting people go. I realize you will not pay attention to this next bit, but I'm going to say it anyway. Somebody else might appreciate it. Eol would not have been a reliable person to have running around on the outside. Granted, he would not have been likely to have told another elf the location of Gondolin because he tried to avoid his own people as much as possible. He might have told the dwarves though. Through them sooner or later the secret probably would have come out. Even if that did not happen, after the Battle of Unnumbered Tears, Eol would have been caught in his wood by Morgoth's rampaging forces and he would have been broken. There was just no upside to Turgon for letting Eol loose and a huge danger.

And Secondly, his 'orders' are a suicide mission in the first place as Gondolin is doomed to failure

So was the whole Revolt of the Noldor, as I have said a number of times. You are not gaining any traction bringing this up over and over again. Would you have preferred they just launch a frontal assault and get it over with? That was certainly Feanor's way. I suppose the poor emotionally stunted Elves could then have "freely" scampered about helplessly as they were getting chopped into itty, bitty pieces.