There's no such thing as a perfect school. Your kids' school has several hundred, even thousand, parents, and there's no way they will all agree with everything the school does. If every policy had to be agreed by a unanimous decision of all parents, they'd never even be able to agree what time to start in the mornings.
So of course you're going to disagree with things. The amount of homework they give them, the severity -- or lack of it -- of the punishments, the stupid uniform they have to wear, the fact that they make them play football even if they hate it, the fact their assemblies are secular, the fact their assemblies aren't secular, making them learn Spanish instead of German, forcing them to play indoors whenever it rains…and on and on and on.
There's nothing you can do about it. Okay you can change schools, but the next one will have just as many irritating little ways. They'll just be different ones. And what's more, there's nothing your child can do about it -- which means that you're just going to make their school life miserable if you encourage them to undermine the system. They'll be in trouble with the teachers and quite possibly made fun of by their fellow pupils. No, they don't need conflicting messages from home and school.
The thing to grasp about any school is that it comes as a package. There are things you like about it and things you don't. If the ones you dislike outweight the pluses, maybe you need to think about changing schools -- that's another issue. But as long as you're there, you have to buy into the package as a whole. And that means that you have to support the school, even over the things you don't care for. You have to encourage your children to do their homework, even if you do think they have too much of it. And you might have to get them to wear a silly uniform, or play hockey, or treat the teachers with respect even if they don't respect them.