We know from various Congressional folks that briefers of Congress have failed to produce any evidence of "imminent" plans to kill Americans Soleimani was involved with that would have made this a legal killing rather than an illegal assassination. The public statements by administration figures have cited such things as the 1979 hostage crisis, the already dead contractor, and, oh, the need to "reestablish deterrence" after Trump did not follow through on previous threats he made. None of this looks remotely like "imminent plans," not to mention that the Iraqi PM Abdul-Mahdi has reported that Soleimani was on the way to see him with a reply to a Saudi peace proposal. What a threatening imminent plan!
As it is, despite the apparent lack of "imminent plans" to kill Americans, much of the supporting rhetoric for this assassination coming out of Trump supporters (with bragging about it having reportedly been put up on Trump's reelection funding website) involves charges that Soleimani was "the world's Number One terrorist" and was personally responsible for killing 603 Americans in Iraq. Even as many commentators have noted the lack of any "imminent plans," pretty much all American ones have prefaced these questions with assertions that Soleimani was unquestionable "evil" and "bad" and a generally no good guy who deserved to be offed, if not right at this time and in this way. He was the central mastermind and boss of a massive international terror network that obeyed his orders and key to Iran's reputed position as "the Number One state supporter of terrorism," with Soleimani the key to all of that.
Of course, in Iran it turns out that Soleimani was highly respected, even as many oppose the hawkish policies he was part of. He was viewed as crucial to the victory over ISIS/ISIL/Daesh in Iraq, much feared by Iranians. Shia take martyrdom seriously, and he is viewed as a martyr. It appears that even Trump took notice of the massive outpouring of mourning and praise for Soleimani there up to the point of people dying in a stampede in a mourning crowd in his hometown. But, hey, obviously these people simply do not understand that he was The World's Number One Terrorist! Heck, I saw one commenter on Marginal Revolution claiming Soleimani was responsible killing "hundreds of thousands." Yes, this sort of claim is floating around out there.
A basic problem here is that while indeed Soleimani commanded the IGRC al Quds force that supported and supplied various Shia militias in several Middle Eastern nations, these all were (and are) ultimately independent. Soleimani may have advised them, but he was never in a position to order any of them to do anything. Al Quds itself has never carried out any of the various attacks outside of Iran that Soleimani is supposedly personally responsible for.
Let us consider the specific case that gets pushed most emphatically, the 603 Americans dead in Iraq, without doubt a hot button item here in the US. First of all, even if Soleimani really was personally responsible for their deaths, there is the technical matter that their deaths cannot be labeled "terrorism." That is about killing non-combatant civilians, not military personnel involved in combat. I do not support the killing of those American soldiers, most of whom were done in by IEDs, which also horribly injured many more. But indeed this awful stuff happened. But in fact this was all done by Iraqi -based Shia militias. Yes, they were supported by Soleimani, but while some have charged al Quds suppplied the IEDs, this turns out not to be the case. These were apparently made in Iraq by these local militias. Soleimani's al Quds are not totally innocent in all this, reportedly providing some training and some inputs. But the IEDs were made by the militias themselves and planted by them.
It is also the case that when the militias and Americans were working together against ISIS/IISIL/Daesh, none of this happened, and indeed that was still the case up until this most recent set of events, with the death setting off all this an American civilian contractor caught on a base where several Iraqis were killed by a rocket from the Kat'b Hezbollah Iraqi group. Of course with Trump having Soleimani assassinated, this cooperation has ceased, with the US military no longer either fighting ISIS/ISIL/Daesh nor training the Iraqi military. Indeed, the Iraqi parliament has demanded that US troops leave entirely, although Trump threatened Iraq with economic sanctions if that is followed through on.
As it is, the US datinrg back to the Obama administration has been supplying Saudi Arabia with both arms and intelligence that has been used to kill thousands of Yemeni civilians. Frankly, US leaders look more like terrorists than Soleimani.
I shall close by noting the major changes in opinion in both Iran and Iraq regarding the US as a result of this assassination. In Iran as many have noted there were major demonstrations against the regime going on, protesting bad economic conditions, even as those substantially were the result of the illegal US economic sanctions imposed after the US withdrew from the JCPOA nuclear deal, to which Iran was adhering. Now those demonstrations have stopped and been replaced by the mass demonstrations against the US over Soleimani's assassination. And we also have Iran further withdrawing from that deal and moving to more highly enrich uranium.
In Iraq, there had been major anti-Iran demonstrations going on, with these supported to some degree by the highest religious authority in the nation, Ayatollah Ali Sistani. However, when Soleimani's body was being transferred to Iran, Sistani's son accompanied his body. It really is hard to see anything that justifies this assassination.
I guess I should note for the record that I am not a fan of the Iranian regime, much less the IGRC and its former and new commander. It is theocratic and repressive, with many political prisoners and a record of killing protestors. However, frankly, it is not clearly all that much worse than quite a few of its neighboring regimes. While Supreme Jurisprudent Khamenei was not popularly elected, its president, Rouhani, was, who obeyed popular opinion in negotiating the JCPOA that led to the relaxation of economic sanctions, with his power reduced when Trump withdrew from the agreement. Its rival Saudi Arabia has no democracy at all, and is also a religiously reactionary and repressive regime that uses bone saws on opponents and is slaughtering civilians in a neighboring nation.