Perhaps people are animals in the sense that we share many common traits. However, people have capabilities which go beyond those of animals, which means we are not ONLY animals. I have to side with Aristotle’s notion that we are rational animals. We can be motivated by reasons, ends and goods, not purely animal appetites
This has to be the most simplistic and errant thing you have ever written. You forget that humans are attracted to many things not merely on the basis of physical appetite or need, but also on the basis of sensible qualities (beauty) and the intelligibility of the object (truth.)
So, there are things (which appeal to purely physical appetite) which cannot become unattractive to physical appetite merely by “changing one’s mind.” There are also sensible and intellectual things, humans are attracted to or not, based upon their qualities of beauty (or lack, thereof) and truth (or falsity) which we can come to realize are not what we supposed them to be and we CAN change our minds about them - even things which we may have, at one time, found physically attractive.
I do, by the way, know that it is entirely possible to “change one’s mind” about what a person finds attractive. Aligning oneself to the truth has a way of revealing the true nature of things and revealing things (or illusions) for what they are, even those which appear attractive on the basis of physical appetite alone. A wise man in once said, “Do not judge by appearances.”
Now merely because you may have difficulty getting beyond pure animal desire does not mean everyone suffers from that same incapacity. You are more than your glands.
The part of the explanation you seem to have left out of “marrying for love” is the accounting for why one person “loves” another in the first place. That “love” does not simply exist a se, it exists because there are reasons and motives (grounded on reasons) for loving the person that come into play. It is those reasons that form the basis for “love.” Therefore, people do not marry BECAUSE they “love” the other person, but because they are moved (emotivated) to do so - ultimately - by the reasons they have to do so.
Your accounting that people “must love each other” is simply shorthand for saying people have an overall “warrant” to commit themselves to the other person which they refer to as the “love” they have for the other person.
It would seem bizarre, actually, to claim that love purely grounded on emotion (sans any rational basis) is sufficient for entering into marriage. It denies the rationality of human beings and makes marriage the most irrational thing any two people could possibly do - commit to each other purely on the basis of some unknown and uncontrollable emotional “attraction.” Marriage, viewed in this way, is not a responsible choice, but an inevitable fate one falls into or capitulates to.
I might allow that I could safely show a preference for chocolate ice cream over strawberry based upon pure emotion devoid of thought or sound reason, but to risk the future happiness of other people (whose well-being I ostensibly care about) purely for some unknown, blind, emotional draw seems - pardon my candor - idiotic, at best.
Personally, I married (over 31 years ago) because I cared deeply about the well-being and future happiness of this woman I came to know and understand, and subsequently made a thoughtful and responsible commitment to that end. Another consideration which came into the decision was the understanding that our marriage wasn’t just about us, but also about the people connected to us whose happiness was also at stake - including our children who, at the time, were unknown participants in that decision. It is this “bigger” view of marriage as a responsible commitment which seems to be unaccounted for in your “being in love is sufficient” POV.
Love isn’t primarily about “attraction.” In Catholic parlance, love is a virtue - one that has the power (grounded in truth) to make both you and the beloved all that you can possibly be. That is why God is Love and, at the same time, Pure Act, the fullness of Being. Love is essentially teleological in that it aims for an end beyond itself, which is why love cannot be purely an attraction, since attractions (in particular physical ones) are concrete and tethered to maintaining the current state of things.
This, by the way, is why SSM is a faux “marriage” since the end of a same sex relationship is, at best, to sustain itself. Real marriage has, as one of its ends, the creation of new life, both in the calling of the couple beyond themselves to become something more than they currently are (complementarity, not sameness, does that) and by bringing into existence new human beings who will challenge all involved to go beyond themselves even more.