No, they are not, if used in a way they are designed to and regularly checked for health.
I think that a proper answer to your question should include statistical information on what percentage of bicycle frames (btw, why only frames? wheels, handlebars etc. break too) break over the time. The reason of a breakage, such as crash or manufacturing defect, should also be taken into consideration. However, I do not possess such information. So instead I want to warn you against being affected by the survival bias effect by only looking at "bad" examples. I want to comment on several points in regard to the video above, or any other bike crash footage.
We do not know how often and how hard these bicycles were crashed before they finally gave in. Damage, especially in carbon parts, is not easy to see without special equipment.
Quite a few crashes in the video were caused by front wheel detachment. That's not frame but fork issue or rather user installation error.
A couple of episodes demonstrate just direct crashes. Nothing is guaranteed not to break after that.
I am not sure that all of these bikes were used in their intended discipline. I've had bad experience riding an XC hardtail on an DH course.
The good thing is, even after all these crashes most of the riders were able to walk away from them more or less fine. That stresses proper use of personal protection.
P.S. Every bicycle user manual that I've read (and I am one of those weird people who actually read manuals to things) states that bicycling is inherently dangerous activity. Not just MTB but any cycling. So, wear protection appropriate to your discipline, know your skills and improve them, regularly take care of your bike, and have fun!