There are risks with everything we do, or not do.
Why is the option of adding the alternate air door available? It is my understand it was to give a pilot an "option", if the air intake iced up.
If that is the case and you don't fly IFR in icing conditions, leave it off, as I did.
If you are worried about sucking in a plastic bag on takeoff, I doubt you will have time to sort out what is going on in time to open the alternate air door before hitting the trees at the end of the runway. Not to mention, what are the real odds of that happening? (I understand it has happened but again, what are the odds?)
In the early days, the air door was held shut by a small magnet and if the main intake was blocked, the suction of the engine would allow the door to open automatically. (I have always wondered if it would open at high power settings while on the ground, just when you need filtered air the most.) The problem was that some of them came apart and some of those parts were sucked into the engine. That little problem lead to the current manual door and even some of those have come apart.
In short, you roll the dice and take your chances.
Since I was building a VFR ship, I left it off and in 650+ hours of flight, I have never given it a second thought.