There is no intrinsic safety problem with two captains operating a flight, given certain conditions.
Provided that they are both equally experienced (recently) at operating in either seat, provided that one is very clearly designated as the commander, provided that the company's CRM courses are geared to this sort of situation.
I can see many benefits of having no "captains" or "first officers" in a company, just pilots.
In other operations, where there is a much more traditional seniority structure, where one guy is used to operating 90% of the time in the other seat, where CRM procedures have difficulty in handling either reverse or level authority gradients, there can be serious problems.
In one of my previous companies, we had a series of runway incursions. In every case there were two captains on the flight deck, one a training captain. The VC8 which landed gear-up at BFS a few years ago was two-captain crew.
As I say, there is nothing inherently wrong with having merely two "pilots" on the flight deck, if the whole ethos of the company is geared towards this. But there are significant dangers if it is not thoroughly thought through.