Seriously...

I noticed when I used to read a camera forum that these flame wars only tended to happen when two things are very very close to each other. When a new camera came out that was clearly superior, not much arguing happened. When a camera came out that was close to another one, huge flame wars went on about which one was "best".

I've read some interesting theories that suggest it's some sort of human behavior to keep group cohesion or weed out similar but different tools or ideologies so that the group acts all as one, specifically in situations where the difference between one thing and another are small to non-existant. But of course, these were the kind of petty disagreements that also sometimes started warfare, so I don't want to make it sound to nice.

I think if we suddenly saw good dynamo's and light for $30, it would be pretty much agreed that dynamos were better, except if you were doing serious racing.

I mean I absolutely love modern dynamo lights (15 years ago they were crap, but LED's completely changed things). But I still use a mix. I'm also fortunate to have a good job and money, so the money vs hassle goes towards less hassle. On my commuter it's definitely a dynamo light. On my winter bike it is as well (it came with a dynamo hub, so dealing with batteries in the cold would be silly). On the other hand my $5k ($3k is what I payed) full carbon bike, I can't imagine putting a dynamo hub on, so I use a Phillips Saferide. I use a battery light on my mountain bike as well, but just mostly because I already own the light. They do make some mountain biking dynamo lights that look pretty cool - not a shaped beam, longer and brighter standlight, etc.

There are reasons for both. No doubt battery lights are cheaper, and cheaper still if you want to transfer them between different bikes. I mean much cheaper then. Dynamo's you don't have to do charging, or deal with batteries that you forgot to charge, batteries that got old and wore out, or even getting lost and running out of battery. They just keep working.

Like I said, I think it's actually that they're both pretty good for certain uses and there's no clear winner which is why these rediculous flame wars keep happening.