A cathode ray tube is dangerous because:
(a) The evacuated glass envelope is relatively fragile. It may implode into sharp fragments that cause injury.
(b) The electrons striking the glass generate X-rays, which are dangerous to health.
(c) The flat face is often made of thick lead glass to make it shatter-resistant and to block X-rays. If the face implodes, there is also the danger of lead poisoning.
(d) It can hold a charge even after you turn it off. You could get a powerful shock.