Because you exclude all other meddling as an explanation. The Kremlin is the other big source of meddling (if you rate them by success in actually changing things, US is on top. Moscow is a distant second, and the third is so far behind it's barely worth mentioning, also it's unclear who that even is), so the assumption is you implicitly defend if you attack US meddling.

Compare to when 2 people are fighting in the playground and you complain only about ONE of them hitting things, without making any remark about the other, or taking any kind of measure to get the other to stop. People like to describe that as neutrality, but of course, it is anything but. Which then gets confusing because people who are badly informed might start to genuinely believe only one of them was hitting, and might even blame the first for all damages. Of course, this is exactly the point of one-sided reporting, even if the reporting itself is 100% true. Even the BBC is doing it these days, little to no reporting on what happens (imho, not because it's going well) in the UK, and "news in support of UK foreign policy" everywhere else. Oh and separate views for UK people and international viewers. And yes, that's in some ways the same Iran does, but there's no bullets or executions involved if you try to get around it, a pretty big difference.

In this conflict the US is defending, let's call it "international liberalism" (in the French revolution sense, ie. laissez-faire), or what the UN calls "freedom of navigation". Which is a euphemism for tax-free international trade over the seas. I get that there are name clashes with for example US politics, let's please not focus the discussion on whether those names are deserving, or who they (don't) match in US politics. And, yes, preventing Iran from getting a nuke falls under liberalism, as in Iran getting a nuke will definitely kill a freedom of navigation in that part of the world.

The other side, ie. Russia/China, if we're only counting UN SC members, is about locking down international trade behind political agreements (which is also a euphemism: these agreements were historically never agreements, but rather the outcomes of wars), ie. letting Russia and China, since they have nuclear weapons, decide who gets oil from the middle east and who doesn't. Through threats.

So you when you attack one side, getting criticized for supporting the other side, is fair. If you don't know the other side, that's called being badly informed, that's literally just dumb and then really you should shut up.