Again, there is nothing scary about it at all. The Challenger boosters did not “explode”, solid boosters simply cannot explode because of their chemical makeup. They can burn like hell, and a seal failed and it lit up the 500,000 gallons of liquid oxygen and liquid hydrogen in the main tank, which did blow up the Challenger.
Solid fuel is a big flare made of Ammonium Perchlorate, and if you don’t have something major to light it, it is not dangerous. It is not an explosive, and in fact if you had 200 tons of it and a blasting cap, all it can do is deflagrate, not explode.
And it doesn’t matter if you can turn it off or not. If you had too, it is too late, so I miss your point.
2 million pounds of solid fuel in 150 foot boosters when lit is dangerous if your strapped under the 3 million pounds of thrust, sure. At least if it was me riding the thing I’d say so. But not because of the explosive hazard.