Is it danger for an aircraft continually travel with sound’s velocity?

Other than obvious logistical problems of fuel, etc. flying at the speed of sound for a long time is like driving your car at high speeds for a long time, except with a plane it can damage the whole plane. You can probably imagine the force applied to all parts of the airplane when it is going fast, especially the wings. Too much stress over a period will weaken the wings to a point where they won't hold the plane anymore.