I honestly doubt that anyone's goal here is to live forever. Even "life extension" does not imply immortality. Most people here take supplements, modify their diet, and go through other measures so as they get older, they are not as physically crippled and mentally incapacitated as those who did nothing or lived unhealthily. To combat aging is the goal, not to live forever. It's not crazy or even unreasonable to think like this.
If your girlfriend questions "why" or "what is the point" of life extension.... It's kind of like asking someone why they don't eat at McDonalds or why they don't smoke cigarettes. If your girlfriend disagrees with living healthily, then she is probably crazy.
If there really are people who think that they are going to be immortal they are either deluded or have death anxiety, both are related to mental illnesses.
Also, most of the people on this particular subforum are concerned with cognitive enhancement rather than life extension. As such, there are many people trying to make up for certain mental illnesses with nootropics (ADD/ADHD is a prime example), which means there will disproportionately be more people voting yes than the response group you are looking for to vote would vote. I'm certain if you had posted this in the Supplements subforum, there would have been a drastically lower number of people with voting yes to mental illnesses.
I have do not have a mental illness and I do not think I'll be immortal. Life extension is secondary to cognitive enhancement for me; this personal factoid shows you are polling the wrong group of people.