"Morality is subjective" =/= "Morality is unimportant and not worth fighting over"
When debating morality with people - usually theists - who believe in objective morality, a common argument I hear is something along the lines of "if morality is subjective, everything is just preference. If someone wants to go raping and murdering, that's just their preference and you can only shrug and take it since no one is objectively right or wrong".
The problem with that line of argument is it rests on the assumption that morality, since it is subjective, is somehow also unimportant and not worth arguing, fighting, or even going to war over, depending on the severity of the disagreement. Notions like "important" and "worth" are also subjective valuations, and I - plus most others, I would contend - consider morality very important, even as we acknowledge it is subjective.
If, for example, there came knocking a horde of marauders who claim a voice in their heads they call god is giving them the "objectively moral" command to kill all a nation's men and take all a nation's women as rape slaves, I and most others who acknowledge morality's subjectivity wouldn't respond by shrugging at their "preference" as they brutalize us, but by grabbing weapons, forming an army, and fighting them to the death to defend ourselves.