Imagine in some chapels in areas like San Francisco or West Hollywood (there
may be none but I'm saying imagine if there were) where the lineup at the
Communion rail might look like a Rogues' Gallery of miscreants.
Or what about a priest going to a prison to say CTLM for the inmates and at
Communion time they all kneel down at the rail, looking like an ID lineup or
mug shots without the ID numbers?
How would you like to be the priest, saying, "Domine, non sum dignus...?"
The priest is instructed to give a short sermon in such cases, about being in the state of grace for Communion, etc. He should basically announce that only practicing Catholics in the state of grace should receive. He might also mention hell fire, especially considering his rather "down to earth" audience.
I forgot to mention that if a priest is in unusual circuмstances (a funeral, prison, etc.) and neglects to mention this, then HE is responsible for all the sacrileges committed at the communion rail.
But, once again, all the priest can do is use his authority to forbid mortal sinners and non-Catholics to receive. If they put themselves forward after all, there's nothing the priest can do about it.
Oh, and sometimes Communion is not distributed at Mass. That is another "safe" path in such circuмstances.