I don't blame you for not wanting Christians to determine acceptable behavior, I hope you feel the same way about groups like the LGBTQ community trying to impose its beliefs on others.
Again, isn't the point of our country that individuals can pursue happiness as long as they don't infringe on the rights of others. But keep in mind, it is a two-way street, Christians have a right not to have their children taught values they don't subscribe to as much as gay people do.
The Supreme Court has ruled on this issue and determined that to the extent practicable, as a society we must try to accommodate different beliefs... the Christian's belief and the atheist's belief and a host of other conflicting belief systems.
Nations can exist only if they can define who they are. Our country is somewhat unique since we are not defined by our ethnicity, but our values. But interestingly enough, our Founding Fathers were so wise, that they saw core values designed for a nation of immigrants with different beliefs as foundational.
What other countries promote individual happiness over you or me being forced to accept group norms? Is gay marriage legal in most countries? What "value" got us to making it legal in the US? Not majority rules, but rather individual freedom.
What other country has passed laws against discrimination to the extent our nation has?
But individual freedom means accommodating biological woman who choose not to share a shower with another biological woman, much less a biological male when it is practical to do so. It should be her decision, not yours or government's decision, who she shares her showers with?
We have free speech in this country, so if you believe a biological female who does not want to share her shower with a transwoman with male genitalia, call her a bigot, but don't deny her the right to personal privacy.
Again, if you don't believe individual freedom, then society does have a right to tell you how you should behave... and if society is predominantly Christian, you are out of luck. But if you believe in the right to pursue happiness, then you need to view things from your perspective and theirs.