I agree that National Rail pricing is absurd. We should fix that. There's this silly two-tier thing going on whereby getting a journey within the Oyster zone is trivial and getting one outside (i.e. most of the bloody country) is this escapade of finding advance tickets, finding the cheapest time, etc.
Ultimately though, things are going to get more expensive. A poster below commented something along the lines of "so only the rich should drive in London" - and that's what's going to end up happening, unless you ban driving entirely, which would be the nuclear option.
Not all problems, particularly those to do with pollution, have an easy "everyone wins" answer. It might just be the case that things we previously considered normal and standard just won't be possible if we want to preserve health and the climate.
There are stations like the ones you're suggesting. Forest Hill has free on-street parking less than five minutes from the station, but that would increase journey time significantly with the switch to another mode of transport with family in tow, and make a day trip much less feasible.
Fair point about some things not being possible though. Better to reduce the number of people travelling if it means a much cleaner, healthier London. I've even considered trying to commute to London from Brighton via bike during the summer, staying a night with a friend and riding back the next afternoon... That would be much nicer if I didn't feel like I was inhaling exhaust fumes for half the journey.
(Feels like it'd be a bloody pain to drive to from Brighton!)
The last part of your comment is what really hits home for me.
People driving private cars around damage other modes of transport. Cycling becomes less pleasant (near passes, inhaling shit, etc); buses are caught in congestion; everything becomes less dense; etc.
(Sydenham is OK as a backup - a bit further south of the station on the side roads. Not as convenient as Forest Hill though!)
Edit: I seem to remember a study about health of cyclists (although don't have the citation so take with a pinch of salt) and it was universally better except in cities. Either crashes, pollution, or both, meant that cycling didn't make a difference to cyclists' health overall.
Please just use the train.
I disagree with your point about public transport massively improving since the congestion charge though. In what respect? I've been regularly travelling in London since the mid 90s and haven't really noticed much beyond the re-opening of what used to be the East London Line. I get the feeling that things are starting to improve now, after some serious public investment, but it still feels like too little. Until peak-time commuters aren't packed into trains like sausage meat I doubt much will shift in terms of behaviour.
Buses have improved, there are far more though I wish they were electric.