Yes, I agree, at least in part.

We are tweaking a multi-trillion dollar system impacting hundreds of millions of people directly and billions indirectly. The impacts of those tweaks take years or decades to (imperfectly!) assess. Many of the tweaks and their impacts are a matter of deep partisan and academic contention.

The system is incomprehensible complex and unknowable, but it’s probably correct and can’t be improved.

What about new tax proposals? Shouldn’t we then reject them all to avoid butterfly effects in this carefully tuned ideal?

No one said it can't be improved.

I'm noting that our political system seems to generate lots of folks going "this is wasteful spending!" when it's… not.

That results in challenges in determining what's a "bad tax" and what's a "good tax", and the consequences of cutting programs may take time to show up.