Terminology is important here. Pedal Clips (refer here) are straps that tighten around the shoe. Clipless, such as SPD have a cleat - refer here
Toe clips are pretty much not used nowdays, so I assume you are talking about SPD style clipless pedals. I do not believe they are dangerous. However, there is a learning curve - it's similar to asking "Is learning to ride a bike dangerous", in that you will get exactly the same answer. Do it in the right locations and take appropriate precautions, expect a few skinned knees and at very worst, a broken bone. Do it in the wrong location at the wrong time, at worst - death.
What precautions - learn to use them in the same place you would teach a person to ride a bike. Avoid heavy traffic - no point falling under a B-Train - and mountain trails with large cliffs along side the track until proficient (Unless you are wearing a parachute) . i.e. Use common sense. Practice clipping and unclipping - and don't venture too far from your safe area until you can do both without looking down (If you look down at you feet, you will fall off). Then - practice "emergecy exits" - Not needed so much for onroad riding, but MTBing, you often need to unclip without expecting it. Eventually you will be able to unclip at any time, without thinking about it.
Don't use mix the use of toe clips and clipless pedals - it will end in tears, as the exit methods used for of each is completely incompatible with exiting the other.