A bird in the hand
Liam, you're right to question whether Catholic schools are necessarily better than public schools or public charter schools. Of course not; there are great Catholic schools, and lousy ones, and everything in between, just as is the case for the other sectors. But where there are strong Catholic schools--particularly those serving non-Catholic poor kids--it's a tragedy to see them going away. Could their buildings be sold to charter schools? Sure. Could those schools be excellent? You bet. But is it harder to start excellent new schools than to maintain excellent schools that already exist? By a mile.* That's why great Catholic schools are worth the fighting for--and worth paying for too.
*Do I sound like Margaret Spellings, answering my own questions? Absolutely.