The reality is, it’s hard, and it doesn’t get easier. Ignore the religious angle for a second, and think of it simply from the perspective of a social interaction. There is a large body of people who have developed a tradition based around certain elements of what they, in most cases innocently, assumed were universal elements for everyone. You are supposed to be part of this community, but at the same time, lack something crucial to how they’ve designed it that excludes you, often on a very profound level. What to do? Have everyone give up this long standing tradition that gives them meaning so that they can be more all-inclusive, and save the religious stuff for those who want it at some other time? Or you just learn not to rock the boat? No matter what, it’s not going to be a perfect situation, and that’s just how it is.
Generally, I have no problem with religious funerals or whatnot. Even if they aren’t to my liking in a particular case, what you have to realize is that this one event is not the only time for communal grieving or rememberance of a person. Any time can be that: at any time at all you can organize your own way of remembering and so on. A religious funeral in no way precludes other things, though generally the religious funeral does monopolize things like the body, the burial, and generally the logistics. But still, no one is hurting you by holding a religious ceremony.
However, I should recall one particular instance when:
a) the friend was not particularly religious at all, but the ceremony was religious (primarily because of her parents, and yes, funerals are really for the living, not the dead)
b) the pastor had 0 idea who she was, and it seemed that his sole purpose was simply to do apologetics for the Christian ideology in the face of a sad event (an early death from a pointlessly cruel disease).
He wasn’t some fire and brimstone guy, some evangelist, he was very well meaning and obviously what he said had great meaning to him. It was simply the fact that, geez, is the point of all this to remember the person, or is it to make sure everyone’s beliefs are maintained in the proper Christian configuration? I mean, what does it matter what someone believes about this event as long as they find some comfort and understanding? It just seemed so odd and misplaced. It wasn’t offensive, it was just… it gave me the distinct feeling of being an alien who had just landed from outer space and was totally confused as to what these strange Earth-people were up to.
That’s life sometimes.
I agree with mostly everyone else: obviously you shouldn’t (and rarely are expected to) participate in holy rituals that do not fit your belief systems, but there’s no reason why you can’t take part in the ceremonial group activities like standing/sitting/being silent, etc.
The real gray area are the hymns. Do you sing about how much you love the lord or not? Normally, I just try to hum counterpoint. 