Well, because obviously they see the progress being promised as unnecessary. If I genuinely believed (or even suspected) that only the act of keeping a hair band on your wrist or enjoying the color green were the keys to Immortality, of course I'd be against scientific immortality because they'd be visibly wandering in the wrong direction like idiots.
I'm actually not religious and I am having trouble with that question. My personal views tend toward Alan Watts' weirdly perfect mashup of science-with-buddhist-elements, i.e. the you cannot kill me in a way that matters mushroom meme, and how one answers that also depends on how they define death and immortality in the first place.
If it's the soul, you're probably religious and the answer is no, because keeping a soul where it isn't meant to stay would be abhorrent to you.
If it's the body, you probably love the idea because you're terrified of nonexistence.
But to not believe in a "soul" and also recognize that matter is indestructible leaves me unable to answer that in a satisfying way. Because, to me, it seems a given that I'm already immortal.
I can physically die, sure, that kid in the ocean exploded. He's not doing too great. But then all the atoms that are me right now will just reform into plants or a bear or something. In Zhuangzi's dream of the butterfly, the answer is both. Or, if you're not the reading type, this quote from a TV sitcom.
Parts of me will be conscious again eventually, and none of me is going anywhere. If you and your family aren't strict vegans, the bones in your leg used to be grass, and now that's alive again.
One could argue (very effectively) that a person is the sum of their memories and that they die when their brain dies, but this does suggest I've died several times now as I form new memories and forget old ones. As I live longer and mainly seem to fuck up more, I have to admit it's an excellent point that doesn't make me less tired.
How do I answer whether an obvious law of the universe is desirable? From my viewpoint, this research is idealogically unnecessary for me, and being forced to spend multiple eternities in only one form, unable to let go of anything that's happened, would be a horrifying trap.