You probably wouldn't. But people do and it seems fine. Turkey and Iran have actually decent train networks now, so you don't even have to go by bus. I think you can go all the way to Zahedan. Cross at Taftan and then bus to Quetta, but from there you can hop on the train again to India, cross to Amritsar and on to Calcutta.
Taftan to Quetta: a bus, leaves before sunset to travel out of the worst heat. Takes about 10-12h. The bus has two massive diesel engines, one in the front driving the bus forward, one in the back to drive the AC.
In the 600 or so km about half of it has some pavement, rest is just desert. The bus does not slow down for potholes, dunes, anything. You jump a lot.
Every couple of hours bus stops, half of the time for people to go in the desert to squat and the other half to pray. Try not to mix them up, could be dangerous.
The route comes within a few km of Afgani border but that does not matter the baluchistan region does not have much of dealings with the central govt.
Quetta is very-very dangerous for westerners, lots of kidnappings. I only found out later, thankfully.
The train from Quetta to Lahore takes about 26h. There is 1st class AC sleeper, 1st class sleeper and second class.
The 1st class feels like it was last updated before independence.
The train crosses wast deserts where temperature is 50C-ish.
This was more than 15 years ago, things might have changed YMMV.