It's typically assumed that lust is a "shallow" emotion, in contrast to the platonic desires for companionship, affirmation, and so forth. Consider the old stereotype about guys "using" women for sex. Such situations are certainly possible, but isn't it just as possible to "use" a romantic partner for companionship or to boost one's ego? In either case, the "user" has only self-regarding desires, to which their partner is merely instrumental. Why the double standard?
Indeed, it seems that genuine lust is, properly speaking, other-directed. It is a form of aesthetic appreciation, a recognition of -- and hence attraction towards -- another's physical beauty. It is genuinely about them and their qualities. It thus seems as "deep" and appropriately flattering as any other form of romantic appreciation.
Perhaps what critics of lust really have in mind is the self-directed state of feeling horny. There the feeling is all about oneself. One wants sexual release, and doesn't much care where it's found. One's partner is then treated as a mere masturbatory tool, a "sex object" in the most derogatory sense. The other is merely incidental to satisfaction of horniness. But for lust, they are centre stage. This is a crucial difference, and one that makes lust rather more admirable, to my mind.
Even granting that lust is about the other, one might still worry that it is for oneself, and hence in some sense "selfish". This strikes me as doubly mistaken. First, I think there is an important sense of lust which drives one to seek not just one's own sexual pleasure, but also the other's. We might call this "unified lust", as the value it seeks inheres in the whole sexual union, not just the part of one lover alone. Secondly, we should not confuse selfishness with self-concern. Selfishness consists in an inappropriate disregard for others. But one can seek things for oneself whilst also caring about others and seeking their good too, so there is nothing necessarily selfish about this.
But the possibility is there, and perhaps this is the real complaint. It is certainly possible to lust after someone without genuinely caring for the person themselves. So lust may indeed lead one to "use" another for sex without having any intrinsic concern for them. This too is to treat the other as a "sex object", albeit in a slightly less derogatory sense than that previously described. (At least with lust they really are the focal object of one's desire. In the earlier case, they weren't even that. Perhaps "sex instrument" would've been a more accurate term!)
However, this possibility is also present with regard to the platonic attitudes. It is possible to "use" one's friends, after all. In the same way, a selfish agent might enjoy his partner for the way she brightens his life, without thereby caring for her or wanting to advance her interests or happiness. We might say that this is to treat her as a "platonic object".
(We can make a similar distinction to that noted above, between platonic "objects" and "instruments", depending on whether the agent's self-interested desire is directed at the other or merely themselves. Note that instruments are entirely replacable, whereas objects are not. For example, one could use one's partner as merely an instrument to boosting one's own ego. Here your partner is merely incidental to the desire's satisfaction. Anyone else might satisfy the desire just as well. Alternatively, you might have a self-interested "objectual" desire for the companionship of that particular person, in which case no replacement could satisfy that particular desire, and that person is centre-stage rather than oneself.)
I think it is plainly more degrading to be treated as an instrument than an object (though neither is very appealing!), but I see no basis for the double standard between platonic and sexual objectification. Am I missing something here?