Challenger and Columbia were lost due to institutional ineptitude. The engineers that were the manufacturer of the SRBs on Challenger specifically warned against the cold temperatures and were overruled. People noticed the foam shedding issue with the space shuttle many years before the Columbia incident. The space shuttle was a catastrophic clusterfuck of a pork barrel political design. There was actually no launch escape system or possibility of recovery from early launch phase anomaly once the SRBs were lit, until they burned out (unlike the launch escape system on Soyuz, Apollo, Dragon2, etc).
The space shuttle had a ridiculous number of moving parts and degree of complexity compared to a Dragon2 on a Falcon9 (or a Soyuz on top of its booster)
The soviet union and russia have had zero fatalities since Soyuz 11 in 1971. I would actually venture that at this point it might be statistically safer to fly along as a passenger in a modern Soyuz mission than to fly as a second passenger in some sub-500-hour pilot's kitbuilt piper cub clone.