There is a world of difference between "If the driver was on the phone, then I do not believe anyone else has a share of the responsibility" and "talking on a phone is bad practice"!
The Berajondo accident, to me, highlights that having a second person, on its own (i.e. perhaps without some strict requirements on the role of that second person) is an incomplete solution to the risk associated with drivers becoming distracted/disoriented, in the general case. As I mentioned in the other thread, it is not the only example, this isn't the once in a million years type of scenario. There are many reasons why a driver might become distracted/disoriented, the possibility of inopportune communication is just one.
Not wanting to sound callous, but if the potential plausible consequence of such a distraction is a freight train (or passenger train even) going off the rails (perhaps at a derail) at relatively low speed you might accept that risk. Historically, we have. If the plausible consequence is that you might run a train load of people into a concrete wall at speeds approaching 200 km per hour, then perhaps your decision is different. Again, not wanting to sound callous, but a decision about what controls you might put in place to manage that risk would need to consider things like the cost of the control against the likelihood and severity of the possible outcomes. Fifty years ago the cost of control may have been exorbitant, today maybe not so.
Rightly or wrongly, a decision on this for that system was made at some stage and that decision almost certainly did not involve the driver (so he cannot be held responsible for it). Other aspects, like track and rolling stock design come into play too, in terms of the likelihood and outcome - the driver is unlikely to have been involved in those either. Even if he was on the phone, pinning him as being solely responsible is far too simplistic.