Some ways that bike travel ( whether it's commuting, leisure, utilitarian like groceries, etc ) helps both individuals are:
* Health for the cyclist, which goes far beyond weight loss
* Usually it's more economical for the cyclist, mainly in gas, insurance, and car maintenance
* While a car or a bike could be faster in different situations, the bike is much less of a hassle in urban areas, especially to park, and trip times are consistent, so that people can reliably make plans
And society as a whole often benefits:
* More trips being taken by bicycle instead of
car means less gas being burned, and less air pollution as a result. This affects everything from asthma rates to climate change.
* Because bikes are so much smaller than cars, especially in terms of width, they need less infrastructure. Seattle is getting ready to take down and rebuild one of our floating bridges, and we're stuck in debates about how many lanes are appropriate for the next 50 years, etc. But it takes a lot more lanes to carry a million cars than a million bikes!
* Congestion isn't the only problem. Bikes rarely create potholes.
* Bikes are quieter, and less dangerous to their surroundings. Neighborhoods are better places to be when there are fewer cars and more alternate forms of transportation. Everybody prefers back streets to main thoroughfares.
Obviously, I live in a major city. Most of what I typically need to do is within a five mile radius to my house, so a bike is a pretty cromulent way to get around. When I go hiking or camping in the mountains, though, a bike stops working; on the same note, if I lived 45 miles from work, I wouldn't think of commuting on my own power. Another caveat is that a lot of cyclists take "joy rides" ( for fun, exercise, or other reasons ) that aren't replacing car trips. I bike around the lake I live on in the evenings pretty often, but not for any particular purpose, and without a bike, I wouldn't be doing this in a car. So it's not that every bike on the street is automatically hitting all of the positives I listed.
Things that would improve the situation would be better sineage to "remind" drivers of their obligations, either wider right lanes or ideally narrower ones and a second lane for passing, and physical barriers. Most drivers cooperate pretty well in sharing the road, and most cyclists are generally polite. But it only takes one. One of my biggest complaints is cars passing too close within the same lane; others are cars failing to yield before making a left turn, and other issues like this. Better protection for bikes in some way, or awareness by drivers, is what I'd love.
I'm not sure what a valid argument against it is ... but I'd say that every idea doesn't need one. I mean, can somebody share a valid argument against the Earth going around the sun?