It's funny, I have also asked that to a lot of people, but I immediately tell them that they will stay young and healthy (but experiences and knowledge will continue accumulating) and that there are enough available pills for anyone wanting them.
99.9% say they wouldn't take it. The usual reason is "I'd get bored".
Then I ask them if the think the majority of other people would get the pill. 99.9% think that other people would take the pill.
I suppose that people really hate their lives, don't dare say that not even to themselves, and they think other people have a much better life.
No one wants to live "forever" (and that's probably physically impossible)-- at least, not in this world-- but people definitely don't like getting sick.
The day-to-day decision won't be "live forever" vs. "die of old age". It will be "get sick" vs. "not get sick" and no one will take the former.
The obvious upper bound on "forever" is the useful life of the universe (i.e. enough negentropy is left to support life). More realistically, no pill will prevent your body from being horribly mangled in an accident and very low risks for accidents pile up to probability 1 over long enough times.
Even then, there will be a small chance of something happening that kills you and destroys all of your backups. Over a long enough time span, the probability of that happening approaches 100%. You could make it a very long time by doing that, but not forever.
Because the universe will end at some point, either getting to a point of maximal entropy, or via a big crunch, or some other unknown mechanism.
One could conceivably escape from this by escaping to another universe - if that's possible - but that's just fantasy at this point. As far as we can tell, even if you can live basically forever you will eventually cease to exist, when the universe ceases to be an environment that's conducive to existence.
So it's physically impossible to live forever. A few hundred billion years is probably an upper bound. Not a shabby run, but not forever.
We can "slow down" the "speed" of time using virtual worlds. Also we can split personalities to have many experiences in the same time. That is providing physical laws cannot be altered in the first place. I think galaxy-wide strong AIs will have better ideas then me, so consider the entropy problem solved.
Most say No.
I then add that everyone else would have access to them too, so their friends and family would also be around. They think a bit more.
Some then say Yes, but some still say No.
I then say they'd go back to a 25 year old's body.
Then they pretty much all say Yes.
The war disappears as soon as you change the conversation. I'm from a secular country though, so I don't what the American Religious Right would say.