I think your wrong - but not dumb.
The core disagreement appears to be whether you see the split between informed and uninformed, educated and uneducated, rich or poor, powerful or powerless to be one of intrinsic capability ( dumbness ) or something else.
I don't believe the vast majority of people are incapable. Capabilities are multifacted and spread via normal curves - there is no separate elite - it's a multi-dimensional continuum, where differences are exacerbated and reinforced by opportunity.
I do think a lot of decision making is more emotional than rational - but that's a self delusion that applies to everyone - and it's what professionals in the persuasion industries understand very well and ruthlessly exploit.
And while this persuasion techniques now scale to the masses, they are still much more powerfully focussed on the elites in power.
ie the power of democracy in the past was while you could powerfully knobble/persuade representatives with targetted lobbying, the people were unblinded.
So take the Iraq war - the UK people thought the 45min weapons of mass destruction stuff was rubbish - millions marched against the war - however the small group of people actually making the decision had been persuaded to 'do the right thing'.
The fact that is was a diaster based on a like was a suprise to nobody outside the bubble, and those in the bubble still seem to think it was a good idea.
Trump just said he'd do the Iran war again given a second chance..... is that dumb or something else?