Short flights between cities in the same country are a familiar part of modern travel, yet they produce a large amount of carbon for the distance covered. I largely agree that governments should replace these routes with high-speed rail, although this should happen only where a fast and affordable train service genuinely exists.
The strongest argument for the change is environmental. A train powered by electricity, particularly from renewable sources, produces far less pollution per passenger than an aircraft, which burns much of its fuel during take-off and landing. On a short route, those stages make up a large share of the journey, so the flight is especially inefficient. If a government ended such flights once a rail alternative was available, travellers would still reach their destination while the country moved closer to its climate targets. Some European governments have already restricted domestic flights on routes where the train takes only a few hours, which suggests that the policy is practical rather than idealistic.
There is also a convincing argument based on convenience. Airports are usually built far from city centres, and passengers must arrive early to pass through security. Railway stations, by contrast, are often located in the heart of a city, so a business traveller can step off a train and walk straight to a meeting. When these hidden delays are taken into account, a three-hour rail journey can be as quick as a one-hour flight, and passengers can work or rest throughout it.
Nevertheless, this policy would be unfair in countries where rail networks are slow, expensive or absent. Banning flights before investing in new lines would simply leave remote regions isolated and push travellers back into their cars.
In conclusion, I agree with replacing short domestic flights with high-speed rail, provided that governments first build reliable lines and keep fares competitive. Under those conditions, the change would benefit both passengers and the environment.