You are right that there is commonly an implicate argument for action on someone else’s part that is irrational. There was originally an argument from Mainline Protestantism* that somewhat bridged the gap from. But most SJWs don’t want the rest of the baggage from Christianity and so don’t want to examine that foundation. But SJWs do commonly carry forward as assumptions ideas like “true” desires aren’t going to be contradictory and therefor don’t need to be put in a hierarchy:

This is not to say that there are many roles [sic] to be filled among those who resist, none of which should be placed in a hierarchy of value. People come from different places of knowledge, ability, and history which makes each person equipped to participate (if they so choose) based on their unique position in society.

In the meantime, the main audience that SJWs are talking to has the cultural value (inherited from Christianity) that we want to increase people’s happiness. So saying you want something, and therefore it would make you happy, is at least some small amount of weight in favor of that thing.

*(God loves all humans greatly and as imitators of Christ we should love all humans too. Also Christ has redeemed people from their sins and therefore they are going to be (and already are in some non-manifest way) made perfect. Since they are made perfect, their deepest and truest desires will partake of the Good. The Good is non-self-contradictory and innately desirable. Therefore these “true” desires, which are in the process of being brought out in them by the grace of God, should be catered to.)