If I think that castling should be removed from the chess rules. Am I a hypocrite when I use it when I play with others?

In the same way proposing laws that would limit legal tax evasion loopholes and using those loopholes is not a hypocricy. They work at different levels.

Wanting to change rules (laws) so that everyone must play with the same rules and using rules until they are changed is not hypocrisy.

Court battle is like debate competition, you can use arguments you don't believe in.