Curious, why should conviction history not be a factor? I could see the argument that previous convictions could indicate a lack of commitment to no longer committing crimes.

Because we as a society decided it creates externalities we don't want to deal with. With a list of exceptions where it actually is important because risk-reward balance is too much.

I couldn't parse the intended meaning from "lack of commitment to no longer commiting crimes"), so here's a response that just answers the question raised.

Do you regard the justice system as a method of rehabilitating offenders and returning them to try to be productive members of society, or do you consider it to be a system for punishment? If the latter, is it Just for society to punish somebody for the rest of their life for a crime, even if the criminal justice considers them safe to release into society?

Is there anything but a negative consequence for allowing a spent conviction to limit people's ability to work, or to own/rent a home? We have carve-outs for sensitive positions (e.g. working with children/vulnerable adults)

Consider what you would do in that position if you had genuinely turned a corner but were denied access to jobs you're qualified for?

The short answer is that it's up to a judge to decide that, up to the law what it's based on and up to the people what the law is.

Sure there is still some leeway between only letting a judge decide the punishment and full on mob rule, but it's not a slippery slope fallacy when the slope is actually slippy.

It's fairly easy to abuse the leeway to discriminate to exclude political dissidents for instance.