Whoever wrote this is (willfully or otherwise) ignorant of the driving conditions on UK motorways. Driving at 60mph is basically impossible - you either have to get in the slow line behind the lorries and go slower, or get in the middle or fast lane and drive ~80mph. Yes, the speed limit is technically 70mph. In most part of the country, nobody gives a crap.
So the range is nearly irrelevant; the car is unsuitable for motorway driving so you won't be taking it any distance at all.
Dark matter has many testable predictions; armchair physicists who think they can second guess professionals only ever seem to know about rotation curves, and smugly decide that they know better.
Modified gravity only has the benefit of fitting certain observations - it has no theoretical backing. With most current data, modified gravity doesn't fit that well anyway. Its largely out of favour with physicists, only with those people who think that without any formal training in the subject they understand it better than physicists
No, they think a small increase in temperature might impact global agriculture and thus mean there isn't nearly enough food to feed 10 billion people. Then people start killing each other for food. This fear is justified.
Its not about air, or temperature, or soil, its about people.
What Mars gets you is a place that is entirely isolated from the poor folks, from politicians who might restrain you or tax you - you can't even access the Internet as we know it from Mars due to radio lag. Its a societal fresh start.
People making your arguments often say things like "why not colonise the Gobi desert? its much nicer than Mars". Thats actually easy to answer - the Gobi desert is (mostly I think) in China, and I don't want to live under the Chinese government. To have a societal clean slate, you need to go far and you need to live under harsh conditions.
Once more, saving 250t of liquid oxygen is absolutely nothing to do with cost! Its to do with reducing the take off mass - which is what enables the performance required for SSTO.
Oh, and the Space Shuttle wasn't reusable, it was rebuildable.
So let me get this straight; you think you have spotted a major flaw in their design that was not spotted by various governments, space agencies and aerospace companies that have thoroughly analysed this project? Have you done the sums and found that the precoolers have more mass than the oxygen saved? Have you worked out the losses due to drag?
I was talking about integrating stages, not payload. SpaceX still have to and always will have to do that. The TPS isn't magic either They are already talking to manufacturers about how to build it. Most importantly though is due to the aerodynamics of the vehicle it will have a much milder re-entry than the Space Shuttle, only needing the same kind of thermal protection it has in certain critical areas.
And no, SpaceX does not have a reusable vehicle that actually exists. They haven't yet recovered a first stage, never mind reflown one.
Please, could people actually investigate this project, its history and the major players who have invested in it before dismissing it out of hand based on intuition?
Wrong on multiple points
It never becomes a scramjet. Not being a scramjet is in fact the entire point behind the last few decades of research. You can either try to burn fuel in a supersonic flow through your engine (scramjet) or you can slow the flow to subsonic and compress it so the fuel can burn properly (ramjets etc.) - problem is, this compression superheats the air. SABRE dumps the excess heat into the cryogenic hydrogen the vehicle carries so that you can operate an engine at high Mach number without its insides melting.
As for too many moving parts; they precooler itself does not appear to have any moving parts. It needs a liquid helium cooling loop to connect it to the hydrogen supply, but that isn't overly complex. Everything behind that is well established jet/rocket engine technology. Even if you assume that each precooler + bypass is itself as complicated as enough engine, the spacecraft only has as many "moving parts" as an ordinary rocket with 4 engines. SpaceX happily flies a rocket with 9 engines and will likely be able to reuse its first stage in a cost effective way.
The reward for working hard is more hard work.