Of COURSE they will, in fact that is the entire problem...
Not everyone can stay at home all the time, and a large portion of the infected have no symptoms.

My mother is staying extremely isolated, and it is very hard on her... but she occasionally must go to the doctor and come in contact with others. The more assholes out there that follow the President's example and words on this and treat it like a hoax, the more likely she will come in contact with the virus.

The statement that wearing a mask " does nothing to prevent infection, they only assist in preventing you from infecting others." is untrue. Masks (depending on the type and usage) CAN reduce you chance of infection, but it IS true the primary benefit is that they greatly reduce your chance of infecting others.

I feel fairly confident that- assuming the filter materials I use are accurately certified- that my home-made respirator is at a minimum better than a n95 mask since it seals tightly to my face and has 3 stages of filtration. I feel fairly confident that it protects me from at least inhaling the virus as much as is possible.

There are other potential routes of infection, of course- but they also can be largely mitigated by proper procedures. Inhalation certainly seems to be the dominant route of infection.