Look at it this way: would you object to people starting a meeting with the traditional Jewish prayer "I thank God for not having made me a woman"?
Or with a collective assertion of belief in Marxism and the eventual triumph of the Communist Party? Or with a declaration that Scientology is the only true way and this meeting will be conducted in accordance with the principles of Dianetics?
The point is, a prayer is an assertion of a belief system. If you happen to disagree with that belief system - and, moreover, you live in a country where it is constitutionally mandated that government should not be bound by any one belief system - are you not entitled to object to someone implicitly dedicating the proceedings to their chosen belief system?