I think the condom is more analogous to a lens cap than a filter or a hood.
Yeah, I guess you don't really want to shoot through a condom, so I'll go with the cap analogy. And your zippered pants are like a closed camera case.
Kidding aside, the filter question will never be resolved. It comes down to a personal preference for what is largely unsubstantiated security.
I always chuckle at stories of how a filter that broke during a lens/camera fall protected the lens from damage. The truth is that the other experiment -- dropping the lens/camera under identical conditions without the filter in place -- is never done. And if an unprotected lens was damaged, how can you be sure that a filter would have prevented that damage? The reverse experiment in this situation can only be done if you have an identical lens to potentially sacrifice.
I will accept that for some bumps and falls a filter ring can protect the lens front threads from damage, but a lens hood will do that even better, and will be cheaper to replace than a filter.
So what about sand, dust and water that gently accumulates on the filter? The argument is that a filter that is damaged from too much aggressive cleaning is cheaper to replace than a lens front element. But who is less careful about cleaning an expensive filter than cleaning a lens? How many people have actually replaced a filter because it was carefully cleaned once too often? And there is the argument that a front lens element may stand up to repeated cleaning better than a filter.
OK, there is the believable argument that a filter will protect a lens from a branch, rock or flying stone chip that in one go scratches the surface. But again, where is that repeat experiment with the bare lens, whose curved thick glass is probably much tougher than that of a thin planar filter? This one is a situation of playing the odds.
I believe a good quality filter will have very little negative effect on an image. Oblique light rays passing through a thin layer of good glass will be minimally displaced by refraction, and internal reflections are minimized by good coatings. The only real argument AGAINST using a filter is lens flare, but that can frequently be handled with a lens hood or shading with a hand or other object. If not, remove the filter.
So what do I do? I have good quality clear filters on all my lenses, and I always use a lens hood. The hood only comes off when shooting with the on-camera flash to avoid shadows of the hood on wide angle shots. I only remove the filter to put on a polarizer because my clear filter has a very thin ring that does not provide enough thread for the polarizer to grab securely.
Oh, one final comment related to the cost of the filter -- does a $200 filter suit a $2000 lens? Absolutely. The filter has much less glass, no moving parts, no electronic chips, etc. I don't think a $20 filter is an optical match to ANY lens, but a bit more money will get you enough quality for most photography.
Remember that an added filter can always be removed when not needed, but a non-existent filter when needed cannot be added.