Small steps :)

I could see it being justified as a progressive measure to increase capacity. Lower the prices , increase demand and get more people on the bus paying fares that you can use to expand service to meet the new demand. Once the infrastructure is built to handle the increased demand then you can make it free.

Vs. if you make it free right away demand spikes with no resources to increase capacity.

Free would definitely be better, but requires solving other problems in lockstep. E.g. homeless people using the busses as a place to exist/stay warm. It disrupts the bus as a function.

A small (deliberately) token fee gets the best compromise. It's akin to charging 10p for a plastic bag. For most people 10p isn't enough to be problematic, in the grand scheme of things. It does massively reduce frivolous usage.

I would prefer pushing it down to £1 return, or even lower, but £2/trip is still better than the current option.

Oh, and just to clarify I also definitely believe we should be using taxes to give homeless etc somewhere better to exist. The busses/trains/underground are not the place for that to happen.

There has been research done into this, showing that free stuff can exhaust a resource like this much faster. E.g. cheap tickets could get drivers out of their cars, but not the people who'd walk two blocks. Plenty of countries with free public transport that seem to work just fine, but you might end up happier with cheap public transports rather than entirely free buses. Not having to deal with tickets would be really nice though, for everyone involved.