Sometimes half measures are worse than none.
There is certainly compassion in providing for women who have been coerced into prostitution to expunge their records, and in reducing the consequences of marijuana use, but there are unintended consequences to both, mostly the belief that in reducing the damage you have fixed the problem.
But in both cases, the better choice is for government to simply get its big nose out of the issue.
Consider, if adult prostitution were simply legal, trafficking would be impossible, as a woman who was being coerced could simply call the police to escape that coercion without losing her livelihood. Marketing, in the age of the internet, is no problem. After all, there is no problem with trafficking of accountants or barbers. Further, no adult prostitute wants to compete with teenage prostitutes, and they are in the best position to learn about underage prostitution and could report it if doing so did not put them at legal risk.
Likewise, decriminalization of marijuana increases the demand for the product but leaves supply in the hands of criminal gangs. If the sale of marijuana were legal and not excessively taxed, legal dealers, who could expect the protection of the police just like sellers of beer and wine, would drive the drug gangs from the marketplace with a lower price and profit margin.
In every case, laws against vices, so-called victimless crimes, simply make things worse, and half measures at correcting the error do the same.