Even if you think what you would say is obvious, please add. This is genuinely something I think makes sense regarding local bus routes given the longevity of light rail and how infrequently routes change, but I also suffer from confirmation bias, so I'm hoping for reasons this would be a terrible idea but obviously would prefer reasons it would be an even more amazing idea than I thought.
CityNerd posted a really good video on this topic a few months ago. https://youtu.be/H6UD9h3hEdk
His videos are primarily US-focused, but I believe this one applies for pretty much any country.
There is also another alternative: cable car. It's a good way to add public transportation with minimal impact on the existing road layout.
But doesn't have enough stops
It's not an either/or thing. Buses are great (if they are well funded) and light rail is also great
The problem with buses is that most of the fleets are still running on fossil fuels. Buses also produce a shocking amount of waste in used tires. 
exactly.
you can't assess the merits of an integrated transport system by arguing which one one mode of transport betters all others.
some places /routes (at some times) might work best with one option.
but most places / routes will be better served by several types at least at some times of day.
buses are one of the most flexible public transport options, fill gaps in space between high capacity modes, and fill gaps in timetables, and they sometimes fill gaps in affordability usually being cheaper.
give them bus lanes and priority at junctions, and they're a lot cheaper and more flexible than trams.
i always think that a busy packed bus lane is making the business case for a train, but filling the gap in the meanwhile. and sometimes a train is impractical.
they didn't only get rid of most of the trams in the uk due to cars wanting more roads. it was also because buses were cheaper and provided much better routes that could flex to travelers needs..
Depends on the road layout; if it's a long straight road then light railway makes sense. It's less maintenance, easier to operate, can move unhindered because it doesn't get stuck in traffic.
For spaghetti road layouts though, I don't see the benefit, but I could be wrong since I'm no expert.
I was initially conceiving this point as a venn diagram, but I guess it works like this as well.
(fuck cars/fuck bikes)
I would think adding railways to places would take a long time, cost a ton of money, and without enough population it doesn't make sense. I don't know what specific area of the world you are thinking, but most of the world is pretty empty outside of major cities, and most of them probably do have rail service.
I have old rail running right behind my house that people always want to start using again. It's in pretty rough shape so the eyes is it's easy to expensive to get it up to spec and the amount of public interest is too low that it become unfeasable.
Buses on the other hand, can get plopped down instantly wherever they will fit on existing infrastructure. They can go where the demands is. You can have a spare one on the lot. I'd think it's easier to become a bus driver than a conductor. And ultimately if you need more buses, just but another, and if you decide to scrap the program, sell the bus and you have no useless remaining infrastructure.
Overall I'd it had the choice to take a bus from A to B or rail, I'd probably choose rail I'd the pickups and drop s were the same, but again, that's also much harder to do with a train. There's room for both, but here I think trains make more sense for longer distances and buses for local.
But why put them on rails? As a kid I remember busses running on electricity from cables that were located above them. Isn't that the best of all versions?
Trolley buses are good. But light railway lasts longer and does less damage to the road for vehicles that actually need to drive. Also you can go autonomous with light railway which is far easier on tracks than without.
They still have those buses in Dayton, Ohio.
Rail has some advantages. Efficiency, Tyre dust. Long term cost. It's a bit harder for the next government to dismantle it. Higher capacity, more predictable path/easier to give intersection priority. Much much easier to automate if given dedicated right of way. Better accessibility.
Rubber wheels have advantages too. Quieter, more flexible (especially with a buffer battery), lower per-vehicle cost can increase the number of services.
I think the first goal should be getting any service that doesn't get stuck in traffic. Then grade separation and consider the tradeoffs for rail.
Those are called trolley busses. They are pretty good, especially due newer ones that have batteries for any needed detours etc
We need a whole host of public transit options that are best suited for each circumstance of a given area. I want public transit so smooth that even if you tried getting lost you end up where you wanted to go with no clue on how it happened. (last bit is an over exaggeration since i don't know how feasible that actually is lol)
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