A private monopoly is accountable to only the owner. May as well be feudalism. In a liberal democracy, government monopolies have accountability to the people. When that is subverted or corrupted, it sucks, but at least there's a mechanism.
There's no such mechanism with a private monopoly.
It is up then to each person reading the records to decide if a crime is old enough or unimportant enough to not matter. That should not be the decision of internet censors or courts who want to sweep their traces under the rug. Or criminals wanting to do that.
If most people think that drug use is not something a person should be trialed for, then the laws need to be changed. Censoring doesn't remove the fact. It just removes discourse to the realm of gossip.
"He who controls the past controls the present, and he who controls the present controls the future."