Public schools are not subsidizing charter schools. Rather per-student money travels with those kids to the school they are actually attending. So since the kids don't go to those schools, neither does the money.

I don't know what state you are in, and there are a number of them where the charter systems are absolute messes and have become fraud paradises (looking at you Florida), but other states things are much better.

Fo instance my kids are in charter schools in California. All charter schools here are required to have tiered lotteries to get in, and after siblings and teachers' kids, the first tier is always kids with an IEP (the problematic/expensive ones). And at my kids school we know one of the kids with a severe problems that the school has bent over backwards to provide the best environment for that little girl.

And every 4 years they have to re-apply for their charter, and one of the front-and-center numbers required for that is how many kids they kick out. And they got grilled on that (which our school passed with flying colors). The charters absolutely had to prove that they are doing things better than the local schools, and our school worked very hard to prove that (and had the numbers to do so). If they didn't, then their charter would have been cut (we heard about other schools that failed this grade).

So I am experiencing a well run charter school, inside a well policed system (California). If you are not, then make that one of the things you cast your vote on: regulations on where your school dollars flow to.

I will note that there is one important advantage that charter schools have: you have to make a choice to get into them. That means that the parents tend to be more involved in their kids' education (if only minority so), and so you get kids that are a bit more motivated to do well. This one area is unfair to the public schools.