Probably not as much as we assume. Space related emissions are 1% of the aviation industry. Also, we just discovered ocean trawling and dredging is the equivalent to the entire aviation industry...
There just is a lot that needs to be done before even worrying about space launch emissions.
Also it's worth noting that SpaceX is using LOX-Kerosone because it's "cheaper" than options which pollute much less (namely LH2-LOX) because the cost of the kerosene is "externalized" and you are correct that something like appropriate taxing could start to fix that issue and force them to make better decisions...