Honestly I'm actually quite shocked at how easily it has been for the media to turn so much of the public against something that's in the interest of most people.
This project will make journeys quicker, increase capacity for more passengers, increase cargo capacity, etc and as a result lower motorway congestion, reduce pollution and the craziest thing is that despite what media barons who are salty they're not making anything off it want people to think it's not even that expensive. The Victorians spent over a decade consistently investing more in the rail network (accounting for inflation obviously), for the first time since the 19th century the UK government have actually properly invested in public transport and yet so much of the public have been brainwashed into thinking it's a bad thing the government are now planning to cut it short because that's what voters want, madness.
There's no reason it can't be both. The new trains will make journeys faster and also boost capacity as the old lines aren't going away.
A simple analogy would be adding an extra inner lane to each carriageway of the M1 where traffic can do 80MPH (legally), faster journeys for those using that lane and greater capacity for the motorway as a whole.