At best, we use objectivity as a bit of scaffolding to hold up the only thing that really can be truth in a film: one's personal experience with it.
If someone says they hate a film because of X, but they love a film that also has X, that cannot be "truth" no matter how much they insist they felt that way. Their feeling can be real, but if so there must be a distinction explaining why they felt one way watching it in one context, and another in another. And their explanations for this can be wrong, or inconsistent with one another. And far from attacking our personal experiences, I think these situations are special opportunities for growth and insight.
If someone says "that's how I felt" to any seeming contradiction or inconsistency, no communication takes place and nothing is elucidated. I've had confusing or surprising reactions to art many times, and every time it served me very well to pay extra attention to those surprises and try to figure out why they had that effect. I would be less of a person, emotionally, if I had just stopped there and said "that's just how I feel, no reason to question it further."
Emphasis on subjectivity, I think, correlates far more with lack of experience and a lack of thoughtfulness. "I just liked it" or "I just didn't like it" are the kinds of things we hear from people who think of films as entertainment more than art. Having a personal experience with something may not mean you can scientifically isolate or mathematically reconstruct your reaction, but that's a straw man if used to dismiss questioning altogether. You don't need a Y-axis to have a "why."
So, if we argue from a standpoint of subjectivity, we aren't throwing up our hands and saying nothing matters. We are actually only beginning to talk about the only thing that does.
There's an old Dave Barry quote that philosophy class is where "everybody decides there's no such thing as reality and then goes to lunch." In any discussion about art we all agree there's no such thing as objectivity but then find a way to judge things anyway, because otherwise there's no point. Otherwise we starve.
If someone wants to go full relativist (never go full re...lativist), whatever, but that also precludes them from meaningfully participating, at least in a way that purports to offer any real persuasion. The moment someone tries to persuade, they are conceding that they believe there to be a shared premise somewhere.