The school should always have the choice of cancelling an event which it believes could endanger or target individual or group safety or create a disruption.
That it has a policy regarding same s^x dating is another and separate issue.
But if the public schools were never involved in so much s(x education except in classes of health, or biology, or home-ec, maybe they wouldn't be forced into decisions which acknowledge that kids under 18 are engaging in this behavior.
And if the feds were removed from state and local funding of education...... perhaps the people could take back the controls of what is taught in their schools and what the community is and is not willing to support and fund. It might even be possible for local decisions to privatize all local schools, and fund them through 'vouchers' from the local school tax dollars, which give both parents and students and the community a greater say as to quality, values taught, and policies. .......Just some ideas.....wondering on alternatives.