This is a badly thought out argument.
The example you provide is not analogous to this situation. The Bureau isn't asking Apple for a Skeleton Key to unlock the door - that doesn't exist. What they're asking them for is to flash the phone with a fundamentally broken version of the operating system that doesn't currently exist and would need to be specially developed from source for this purpose.
And to what end? What if Apple
do capitulate or get forced to do it? What kind of tinpot terrorist organisation is going to "stick to the plan" when a person that apparently knows, in great detail, the entire plan has been arrested by a government agency with an alleged history of complicity in methods of torture and unlawful interrogation? Anyone with a bit of common sense would have to assume that the entire operation is compromised and that any element of the plan - people, method, location etc. was likely to be now known in detail by the enemy. So what's the first thing you're going to do? Abort, go underground, burn everything and start again. This is counter-intelligence 101 - it's not rocket science. Even if the Bureau got hold of this data, its likely intelligence value at that point would be practically nil.
To think that this request is a "one off" is frankly naïve - you don't get a capability like this once and say "never again"; you wheel it out repeatedly - "you did it for this terrorist, now you should do it for this terrorist and this bad guy, and while you're at it, all of these criminals' phones..."
And as for the notion of holding the executives of Apple Inc to account if there is a terrorist attack, how can you prove that their "non-compliance" was the root cause of that intelligence failure? Good luck prosecuting that. Without the contents of the phone available, it's not possible to make that claim.
And besides, the Supreme Court forces big tech companies to unlock their devices on demand, what are the bad guys going to do? Change their tactics. Everyone else suffers while the bad guys keep doing their thing, just in a different (and uncompromised) way.
This is a cat and mouse game that traditional law-making cannot outmanoeuvre and any attempt to do so has a high price for the liberty of law-abiding citizens while delivering practically no benefit to our security. It's a fallacy to think that curtailing people's rights and endlessly making things illegal are going to stop people that are willing to take the most extreme illegal courses of action to achieve their objectives.