We can't just sit here and do nothing. TK was on the edge, everyone could see that. He was sick with worry about his brother. Since no one was willing to take the strong-sensible leader role it was natural for Tai to claim it. Someone needs to be cool and strong.
Someone needs to get everyone together and think of a plan.
All of us. Mimi and Sora looked like they were ready to burst into tears any second. TK was 'angry' and that was an understatement. He was nervous, scared and angry. He wasn't less scared or worried for his best friend but he needs to be strong.