It’s a pretty standard take that men should be contributing just as much to relationships as women do. They should be providing equal time, energy, attention, labor (domestic, emotional, sexual, or otherwise). The controversial part is demanding equity when men fail to provide equality. If he’s not going to bring exactly what you’re bringing to the table, why shouldn’t he bring something of equal value?
If you find a man that adds value to your life without subtracting any, if you find a man that puts in all the same effort in all the same ways as you do, who does just as much work for you as you do for him, that’s great. You are both providing sexual and emotional labor (aka work) for each other. But how many men do you really know like that? How many of the men in your life honestly fit that description, even when they try their best? Unless you want to give pieces of yourself away until you are spent completely, you need to be getting something back. So you can either cut down your labor to match theirs (for most m/f relationships, this would mean 0 or negative labor), OR you can charge for the difference.