Maybe not entirely seriously, but there is a direct causative path initiated by the United States that you can follow which lead to this result.
Iran shot down this airliner after mistaking it for a cruise missile launched by the US, which was arguably a credible fear given the events of days prior. If the US didn't assassinate Qasem Soleimani (with a drone, near an airport), Iran wouldn't have made this terrible error, as they would not have made a retaliatory strike.
Additionally, you can go even further back and argue that if the US didn't withdraw from the nuclear deal struck in 2015, none of these events would have taken place.
There’s a direct causal path from any event to every event in its future light cone. You need more than “if not X then not Y” to blame Y on X. Otherwise you end up with ridiculous things like saying your cat saved your life by barfing on the carpet because cleaning it up made you late for your bus which crashed.
This is absolutely a counter. There would be no assassination of an Iranian general in Baghdad had he not commanded the insurgency with the sponsored militias in Iraq.
That sounds like "another critical factor". A chain of events led to this. The parent is saying "one link in the chain is US involvement", you are saying, a different link in the chain is Iranian involvement. Both can be true, and neither invalidates the other. You've done nothing to invalidate the parent's post because you haven't removed their link from the chain, you've just added other salient links to the chain.
Stop treating blame like it's some simple, single element. It's a complicated, multi faceted chain of events.
If country a starts a war and then country b defending itself accidentally shoots down a civilian airliner it’s ridiculous. It’s ridiculous. You’re saying it’s completely ridiculous to blame country a?
Yes. We rightfully expect people with guns to have an idea of what they are shooting at. Firing wildly at anything that moves tends to earn condemnation.
If you qualify country A's actions as "starting a war" then country B had started many dozens of wars themselves in the previous decade, and subsequent one.
That's basically my point. Ultimate responsibility lies with those who decided to fire a missile at a civilian airliner without doing any due diligence or applying common sense, not those who "created tension" or whatever you want to claim the US did in that situation.
No one can rationally argue that that was partly the US' responsibility, though.