Newsflash- we're not bringing Tiberium fuel cells into space. The public is upset we're building some on Earth. We will flat out lose our job if we put a single Tiberium fuel cell into space.
How many Somalian pirates do we see hijacking shipments of nuclear weapons material? How many people are offended at the idea of governments responding to attempts to steal nuclear material with lethal force?
The idea you think it takes micromanaging every single human when the government has a monopoly on the use of, refining of, and harvesting of tiberium is the real baffling part.
You and I are talking past one another. You can't concieve of the government being so overbearing about Tiberium, I'm saying it already is- that we have received warning shots across the bow for our actions, and that we are laughably far from seeing LT-power plants spread. There's a decent chance the literal 1st phase is the last we ever do, and it's possible that doesn't even finish.
Why on Earth would GDI not check every single ship going through the relay as a matter of course? Or stopping at Earth? Or Venus? You seem to be under the impression there's going to be a bunch of commercial traffic to hide among? There's going to be a major tariff barrier with Citadel space, the relatively specialized cooperatives, and then there's going to be state-owned corporation efforts- which by their very nature are going to allow a lot of government oversight.
Moreover where are they going to get in contact with the very few corrupt humans that are in a position to a) be contacted, b) get the material, and c) have the resources to deliver this, d) can hide all this super incriminating evidence from InOps. This is not an instance of someone stealing a bit of gold out of the mines, GDI is going to vet every single person involved with gathering Tib. And with EVA and AI, it's going to be increasingly hard to find these humans with government background checks who are hilariously corrupt and amoral enough to proliferate the thing that's universally blamed for the death of billions.
There are several worlds of distance from material 'randomly' falling off backs of trucks and stealing Tiberium when we're at the point of being in contact with ME.