We can't force people to roleplay a certain way. If they want to go down the path of ultra realism, that's a choice that they made and nobody can tell them otherwise.If the server moves towards a medium-heavy rp direction, I believe that every faction should also embrace that and not have their standards higher than the server recommends. People that will be oriented towards medium RP, they'll probably lose any kind of interest in the server because they probably won't be accepted in different cliques and so on. Goes for illegal and legal factions.
Generally speaking, server staff ought to enforce that the minimum required quality of roleplay (med-heavy in this case) is maintained, anything above that should not be regulated or discouraged in any way, considering that it regards groups and not the community as a whole - and of course, as long as it's not being forced upon an entity or group by other entities or groups.