Disclaimer: This work was not intended to make a profit off of the works of others or any profit at all. Digimon is not owned by me; please support the actual series.
It was the first Digital Law passed by the UN that Tai had had negative feelings about. It penalized digimon who protected their partners too well. It was Digital Law 37 and in layman's terms it and its complementary laws boiled down to: "It is illegal for any Partner Digimon to be discovered above Champion level unless there is a threat of Digital Origin that merits the use of the level. Whether or not it was required will be determined by a committee of UN officials after the treat is over. After the end of the threat all digimon are to revert to at greatest Champion level."
And now that was coming back to bite them as Alex literally COULD NOT change back. Sure he doubted that anyone would OPENLY condemn his son but the attacks would be implied and from all sides. And that was if they decided to play nice. It would be horrible- but not unexpected if someone arranged for Alex to "disappear" –only to reappear later as a dead husk pre-empting a rise in Mega-soldiers.
For this main reason they were trapped. By calling Alex a human-digimon hybrid they could likely exempt him from the law as Hybrids have no restrictions. However unless they were careful and played their cards perfectly it might also condemn his child to slavery as Hybrids also have no rights. One incident- that would be all it would take- one disavowed incident by black ops and Alex might be forced to lose his home.
Tai Kamiya was not stupid. He had been playing this game ever since he graduated from college. He knew a bad hand when he saw it… but he also knew which hands he was backed against the wall and the only thing protecting everything he cared about. This was a time when it was both. Well he could amend that- he was not the only one on his side in this- but they had a bad hand and couldn't afford to lose. It was done. Everything rode on this. The match: Sudden Death, Penalty Shot- now up Taichi Kamiya. All that remains- to bury the ball in the upper-left hand corner of the goal. 'I won't miss. I can't afford it!'