You want everyone protecting themselves in some way (even a homemade scarf) to reduce the odds of spreading and reduce the viral load if there is spreading.
Even the worst homemade mask is better than nothing, and in a group setting every little bit helps the group environment.
This is a classic case of “the perfect is the enemy of the good”.
In this thread, where people come for solid info we need to make some clear distinctions on wearing masks, especially for younger and older people who do not quite get it.
No. 1: if you are wearing a mask because you are not infected and do not want to be, YOU MUST WEAR IT CORRECTLY. That means having fit your face properly, knowing how to take it on and off correctly, and for some masks how to disinfect it immediately after taking it off. Anything less than that offers you little protection and possible harm. If you touch your face to adjust your mask or pull it down to breath you blew it. Think of trying to train a child to follow infectious disease mask protocol. Good luck with that. Most people, who are not infected, will be safer not wearing masks and staying away from everyone. Unfortunately, if wearing masks decreases social distancing, more infections, not fewer will occur. This has been the debate in the CDC and elsewhere.
2. If you are infected, with symptoms or not, whether you know it or not, wearing a mask is good. Wearing anything over you face is good. Anything you do to slow, disperse, contain, partially contain your respiratory vapor is good.
So this is the dilemma. Because many may be asymptomatic, and because we don’t know how many, everyone will have to assume they are infected and wear a mask. This will decrease respiratory vapor. But if all the other protocols of social distancing, hand washing, not touching face, sanitizing, etc. are not kept up the net gain may be a loss.
In sum, your mask offers you no increased security unless you know exactly how to do it correctly and you have a supply of approved N-95 masks. See https://www.cdc.gov/niosh/npptl/pdfs/UnderstandDifferenceInfographic-508.pdf
Having the infected wear masks is a good idea.