The whole regressive tax argument is a load of crap. Just make some other tax more progressive, and you are done with it.
The argument that a fuel tax hurts the poor just allows people to pretend that their opinion is based on compassion.
One could just as easily argue that low fuel taxes combined with ethanol laws hurt the poor. We are now looking at displacing large amounts of fossil fuel with bio-derived products. This increases demand on food products and increases basic food costs. Low fuel taxes also create a market that produces very large cars. Higher fuel taxes would mean that smaller (cheaper) and more fuel efficient vehicles would be widely available.