My point (which I made earlier) was of two parts. I'll emphasise the (much shorter) first part again: If there is no tangible evidence to 'prove' something one way or the other, then, your argument, as much as mine, is invalid (if it must rest on concrete proof). I would say, if immediate evidence of collusion isn't evident, then, we must look as what most closely approximates to a convincing explanation. How convincing that is depends on ones ability to understand politics. The second part of my point was my attempt qualify that. You however have no second part; you only restate the idea that there is no 'proof'. And by doing that you do not make a qualified judgement. Instead, you prefer to trust authority despite a lack of forthcoming 'proof'. In this way your reasoning is circular and embodies the prevention of conclusion - the case must be left open until there is 'proof'. And by your account there cannot be any.
Quite a predicament (and a headache). Instead I prefer to suggest those in the know are responsible.
With this kind of thinking, one could claim that there are still WMD in Iraq. No one has found evidence of WMD, and, like UFCo's possible direct involvement in the '54 overthrow, few published scholars believe it. But Hussein had shown an inclination to obtain them before and he had a motive to do so, thus, for you to be logically consistent, your idea of "intent" should lead you claim that they must be there, despite any solid evidence in support.
A historian is irresponsible to claim something as a fact without evidence, despite his or her personal feelings that it may have existed. The best that you and I can say is this: "UFCo may have directly colluded with the US government in overthrowing Arbenz (and leading to decades of death and instability in Guatemala), but no one has yet found direct evidence of this (yet)." To say "UFCO directly colluded with the US government in overthrowing the Arbenz government because they had a motive to do so" is misleading and false without evidence.
I'm no apologist for the company. It did a number of nasty and racist things, but it also set up the first clinics and schools in the areas where it operated and brought relatively high paying jobs in places where people barely got by on subsistence farming. The history of this company belies any easy categorization or moral judgments.