What about a software bug that was actually a deliberate "backdoor"? Or what about a tax statute that was written with warnings that it was ripe for abuse (e.g. the pass through income tax cut)?

That some bugs are deliberate has no bearing on the non-deliberate ones.

That supposes that there was no intent to leave the loopholes in. "It's not a bug, it's a feature"

It's rather difficult to determine the intent of legislators, especially after some time has passed. Courts sometimes look at Congressional debate transcripts when deciding complex issues of federal law. But different congresspeople often have different conflicting intents even when they vote the same way.

Sure, especially with respect to some edge cases, and that may be an argument for not throwing people in prison that exploit certain loopholes.

On the other hand, there are certainly cases where a loophole is obviously not the intent of the legislators, and regardless of the legality of exploiting it, one could justly view exploiting it as immoral.

For example, sticking with the analogy of computer bugs, a multiplayer videogame that has an obviously unintended glitch, which lets you cheat against your fellow players.

If there was no intent to allow companies to get away with this, then these tax escapes would have been closed once they were abused. But they are not closed, because they were left there intentionally due to lobbying.