I think your drifting into all-or-nothing thinking. No filter system is absolutely perfect, ever. And attaching any filter onto a human only makes things worse. It is pretty well understood full-face gas masks and hoods have a certain percentage failure because the wearer fails to get it on correctly. And even when all procedures are followed human skin isn't an ideal material to seal to. As the person moves small leaks are pretty much inevitable.

What gets lost is that in most cases absolute perfection, while desirable, is not necessary. We are often surrounded by toxins and infectious agents. But the body is not entirely defenseless. A single bacteria has little chance of survival on its own. It is pretty much a sure thing that everyone has some exposure to infectious agents if they are present at all. Only a few of those exposed, those who get exposed to large populations, typically millions in a droplet that can give the infective agent a localized quorum within the body, suffer. As with anything else dose is critical.

The same is true of chemical agents. Protective equipment doesn't entirely eliminate the agent. It just keep the exposure to an acceptable minimum. In this even a simple filter mask shifts the percentages in your favor.

Don't think that just because you can't obtain some idealized protective system that it does no good to use a simpler system. A simple cloth mask has an effect. Don't fail to take advantage of what you have on hand and what you can get now because it isn't as good as what you would like to have.