Since you mentioned churches: keep in mind that anybody who believes in bodily resurrection will have a problem with their loved ones being buried without heads.

Anyone who believes in a resurrection that is so fixed in nature that their deity will have trouble resurrecting the person if the body is in two pieces is probably so far removed from rationality that it probably isn't worth trying to convince them that cryonics is reasonable. (On a marginally related topic I've been thinking on and off of the halachic(Orthodox Jewish law) ramifications of cryonics and I think an argument can be potentially made for cryonic preservation as long as one does full body preservation. It might be interesting to talk to some Modern Orthodox Rabbis and see what they say. Judaism has generally been more willing to adopt new medical technology than Christianity so if one is trying to aim at religious individuals that might be one possible avenue of attack. ETA: Thinking slightly more about this, I think a strong argument can be made that if halachah allows for cryonics then halachah would actually mandate it (based on the rules about the measures one goes to save lives))

I suspect that among the less strongly religious, such as moderate Christians and Jews in the US, religion is not itself a major reason against cryonics. I suspect that the weirdness aura and cached thoughts about death are much larger elements.