Frankly, the idea that portals using Space Magic Materials to break physics as we know it, cannot break this one specific aspect of physics, seems pretty silly to me.
In short, don't get hung up on a specific element of things, it works.
What it comes down to is that conservation laws aren't just physics, they're
metaphysics. They're underlying mathematical assumptions that go into the idea that we can even
have physical laws.
A lot of science fictional stuff just violates the laws of physics as we know them, which is fine. So did radium, once upon a time. So did the precession of the apside of Mercury, once upon a time.
Once upon a time, it was a "violation of the known laws of physics" that every time you open an oven door you don't get zorched by a blast of gamma radiation; this was generally interpreted as evidence that we needed better laws of physics. Better laws of physics were duly devised, and that's part of the story of how you are reading this on a computer, because we wouldn't have computer chips if Max Planck hadn't felt compelled to "git gud" due to the problem I just described.
There is ample precedent for new scientific phenomena to defy our understanding of scientific laws.
But the conservation laws are so fundamental, they're right up there with "cause and effect" itself in terms of our understanding of how reality works, and importantly,
doesn't work. Once they go out the window it causes a lot of upheaval, both in practical terms and in conceptual terms like "so what can we confidently say an unknown phenomenon is and is not capable of?"
...
For instance, tiberium grows by converting existing mass at the atomic/subatomic level. This is generally understood to be impossible by today's science. But even if it
is possible, we can still
have coherent mathematical laws describing it, in principle.
Without conservation laws, preserving that kind of coherence becomes much harder.
uh oh
think of the truce and all the diplomatic efforts we have made there
that not good
Given the context ("and then Director Granger's generosity bore fruit,") it might actually be foreshadowing something
good, not something bad.