bottom line... a lighter bike is all personal preference. Will an extra $3000 and a 2lbs lighter bike make you any faster or better? Well a very insignificant amount but most weight weenies do it for bragging rights or just because they can. People who want that light bike but can't justify it will criticize them.
My 2 cents worth.
Just gotta emphasize this.
Guys, we don't need to hear, yet again, stuff like "it's your weight + the bike's weight" or "take a dump or leave the water bottle home to save a couple of pounds" or the worst: "the cheapest way is to lose weight yourself".
Yea, yea, yea, we know that, it's not the point.
We like to build light bikes just because it's fun to do that and they're fun to ride. And, we can afford spending a little money on this fun hobby of ours. Believe me, although I have not always felt this way, if you put even a really expensive bike in context of other hobbies guys have - boating, fishing, golfing, guitars, snowmobiles, atvs, car stuff, audio equipment, christ, flying!.... you name it. ..... a few thousand $ for a bike, while expensive for some (believe me, it's been totally out of touch for me at many stages of my life), really isn't a huge expense for a healthy fun hobby. And for some of us - within what we can afford - it is simply fun to learn about and find parts and put together a lightweight bike.