Many of the things touted as "harm reduction" are zero-sum (they benefit some and harm others).
Unions tend to be nationalistic and limit membership to natives. "Universal" healthcare excludes non-citizens, requires immigration restrictions and costs are offset onto uninsured groups. Public transport makes it easier for states to control borders and it's run inefficiently.
Support for such policies typically stems from ignorance on how they work or from favoring certain groups over others (including oneself).