In the past, I would sometimes point out Matthew 6, verse 5-6:
6:5 And when thou prayest, thou shalt not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward.
6:6 But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly.
Christians tend to ignore this passage or interpret it to say that an organized prayer in a church is fine since everyone there is praying en masse so the whole church or event is a 'closet' shared by like-minded people.
However, what Christians really are neglecting is how organized prayer is really interrupting their personal relationship with Jesus and their freedom to pray whenever and however they want.
If they truly want freedom and a personal relationship with Jesus they should be demanding that they be free to say whatever prayer they want, in any way they want, inside their own minds. When a person of authority leads a prayer out loud they are infringing on how a believer can speak in a personal way to Jesus.
This now has become my argument against prayers in schools, at public events or during Town Council meetings. If time for a prayer is going to be allowed, every praying person must be free to say whatever prayer they want. It is an infringement of a person's freedom to have a directed prayer or to be coerced into saying the prayer the leader chooses.
If I step into a church and an organized prayer is going to be said, that's fine since I have opted-in to be a part of how this church conducts its rituals. However, because public places are open to everyone, no one must give up their freedom of mind or conscious so that another person or group can impose their prayer on those around them. Even Christians should be offended that someone else is telling them which prayer to say during their personal conversation with Jesus.
I don't oppose a 'moment of silence' to open a public event since I am free (and are believers) to do whatever mental ritual I want (or not) without interference. A good example is the two minutes of silence on Remembrance Day. During these two minutes, I can remember the great wars (or not) in any way I want. I choose to think about my grandfather that fought in the First World War. I'd be angry if some person or group demanded I take part in their memories.