So when was the last time a private school paid a dividend ? That's what businesses do. Yes let's make it unviable for a lot of these schools to operate and force more kids to use the state system that their parents are already paying for but not using , let's add even more kids to the register without any extra money to pay for them, typical flawed left wing politics of envy.
I'd be curious to know what portion of fee paying parents would no longer consider private schooling if they or the school didn't get tax breaks, forcing fees upwards? I know these people are not all millionaires, but money is really not an object for most of them. Being pragmatic and removing any envy (or accusations of envy) from this, the answer to that question should provide the answer as to whether tax breaks are sensible. It should come down to what costs the government more money - the loss of tax income, or the extra burden of those kids to the state, who would go to private schools if the tax breaks existed. I don't know the answer to that question.
Incidentally, why is it that in an industrial powerhouse like Germany, the idea of paying to send your child to a private school is completely laughable whereas here it appears to be something to aspire to for some?