The situation that is dangerous here is if a power source were to be connected to one of these inlets and it did not have a sufficiently-sized breaker and the other side has a dead short, you are looking at a fire inside your walls.
I just installed a 50 amp generator inlet on my main panel, and even though my generator has a matching 50 amp circuit breaker, I installed a separate matching 2-pole 50a breaker on the inlet circuit. This protects the electrical system from even the most screwed up of generators being connected to the panel.