Mercedes have always allowed their drivers to race when the circumstances were right. Like other teams, when they needed it, they have operated team orders. It is a team game and their aim is to win the constructors' championship (because it is that which brings in the most money).
By contrast Ferrari (remember them?) have virtually always operated with a "first" and "second" driver (though not lately because it hasn't really mattered too much). This was especially so when Schumacher and Alonso were their number ones. Remember (when team orders were illegal) Rob Smedley's famous "Fernando is faster than you" uttered to Felipe Massa. Massa had been leading the German Grand Prix for most of the race but Sebastian Vettel (in a Red Bull) was hot on the heels of second placed Alonso. The call allowed him to take the lead leaving Massa as rear gunner to fend off Vettel for the remaining laps.