I have seen and fixed many of these cracks. From experience, I wouldn't consider it a safety issue.
Those will say that any amount of lead in their water is bad and by such standards the word safety has to be attached to any problem with suspensions BUT, in all the cases where total failure occured (the crack servering and the control arm folding) it happened at low speeds. This is NOT an accident. The loading of the affected area is probably tens of times higher during slow speed turning than at high speeds. The only exception to this might be potholes at high speed.
The part always breaks in a parking lot.
Bosch Master, ASE Master, L1
33 years MB technician