IMHO the trouble as usual is the compromises and alternatives.
You take 30 truck's carrying 50 bikes, a load of kit, enough fuel for 10,000 people to sail to America and you drag it to a race circuit. 5000 people then clog the roads and burn even more fuel to watch 20 blokes finish exactly where they set off from. This isn't very good for the planet.
So, lets make it greener, only burn ethanol and hydrogen and do circles to see who made least noise and least pollution and used least fuel. The crowd will at least use less fuel as they mostly only came in the first place only for the chance to see some bloke wearing half a dead Kangaroo slide on his **** at 120 mph. They'll use their fuel instead to visit the local IKEA and buy sliced dead tree's trucked in from Scandanavia. Trouble is, the ethanol is made by a dictator in South America who's population are now half starved as their food is turned into fuel and they'll have built an atomic power plant on every street corner to electrocute sea water and make a bit of H2.
The truely green alternative is to sit in a dark corner and imagine the race bikes. However, this is not what we humans are any good at as someone will soon go build what they imagined (and it might be a bomb not a bike!). The only solution then is to murder and compost half the population, this providing proper green entertainment for the others. I'd therefore like to suggest Roman style games (but not chariot racing as this requires Osterich feathers to go with the Kangaroo skins) as the true green alternative to bike racing

As it seems joined up thinking isn't going to happen, I'm thinking it's far easier to just take small steps and see what happens next. We should try the new fuel ideas, try transport solutions like park and ride for the crowd. Motorsport is part of the solution as well as part of the problem I think. We've hit the limit of the resources this planet has, so we need to get smarter in how we use them.
If technology doesn't provide the answer via some miracle fuel, the planet typically finds a way of removing the offending species anyway!
Andy