But Seifer didnt know how many were in there. He just rushed in, blowing everyone's cover and screwing up the plans the others had made. They wanted to do things as discreetly as possible so they could complete the mission (if I remember right, Rinoa wanted to announce something over the tv, I think the freedom of Timber) and have time to make it out before serious reinforcements showed. When Seifer burst in (on live tv), he alerted all the other soldiers out there to head for the tv station, because the president was in danger. Not at all discreet.