Train-advocates being against self-driving cars will be recognized as being equivalent to environmentalists being against nuclear power. Fortunately, I don't expect train-advocates as being nearly as successful. Once someone has tried Waymo, there's no going back to the old ways.
But you're ignoring the core point (in both your metaphor and in the argument at hand):
- If everyone took a Waymo... Waymo sucks. Not true of trains.
($/MW of power is stupid with nuclear in the age of solar and batteries, with basically zero safety concern... i.e. you can deploy solar and batteries to houses... not so much for nuclear)
All take Waymo dedicated taxi - it sucks just like cars in heavy traffic.
All take Waymo shared taxi/minibus - it is better than current mass transit and almost as good as car during low traffic.