I don't know what a siddur is. I've met ex-Christians who nevertheless have good things to say about prayer. I can't relate to any of this. If you gotta do it, maybe it's best to pray in a language you don't know.
He's basically taken the prayerbook and removed God from it. I find it interesting, and definitely intend to get a copy, both a copy of the Hebrew and a copy of the English (when it's released) just out of curiosity.
Yes, I think you're right. I've attended labor seders, which were not limited to Jews, but included blacks, Africans, Latinos, and others involved in the labor movement. Ceremonially, they are rather lame, and overly didactic politically. I appreciate the spirit, but even without religious content, the attempt to convert a religious occasion into a socially conscious occasion is kinda weak.
Rabbi Sherwin Wine, the founder of Humanistic Judaism, said that Judaism is like a tapestry, you decide for yourself which threads are relevant or useful to you, and you leave behind the other threads for others. I don't know if turning a religious event into a social event is necessarily a weak idea by definition, how well it works might depend on how creative the organizers were and maybe also the energy in the room from how well everyone got along with everyone else. You could have two seders set up the exact same way but the energy at one might be very different from the energy at the other seder and that could be enough to spell the difference between a seder that was successful and one that wasn't. I think the labor seder you describe sounds like it was more a political event.
If I had a seder, I would invite friends and organize the seder so everyone felt included, but I'd keep the whole thing a small event, just a few people, or it doesn't feel like an intimate event anymore. I'd also only invite friends who I thought would get along really terrific with each other.
What Rabbi Sherwin said for Judaism is right for all religions. Infact people usually take the usefull threads and leaves or ignore away the rest. I find it being done at a very large scale at all levels with Islam in my own society. I often wonder if it is a useful tool for fulfillment of intrest.