Sure the public opinion is affected by PR efforts, but people still possess facilities for critical thinking, and everyone knows to be critical about political claims rather than take them at face value.
Voters might want lots of things, but do they get them though, when those things don't align with what those in power want?
/s
who's "they"?
People with this kind of power and money form a series of formal and informal interlocking networks, and often interests align across most or all of those networks. Tax cuts for the rich and for corporations is perhaps the most obvious one. Pushing for war might be a bit less unanimous, but wars do produce near-immediate profits for the military-industrial complex and those invested in it, and potential future business opportunities for other sectors (for example if the war results in regime change, which leads to an opening of previously closed markets, the sale of state-owned businesses and assets, etc).
It is also clear who is telling the media what to say.
The one thing that is not clear at all is how much the media actually influence voters. I don't think there's as much influence as the OP was trying to convey, but well, as I said, this is not clear.
The voters vote what they're told to -- and they're told to by those in power who can pay for campaigns, have their pals in party positions, etc.
Plus, the voters get all kinds of stuff that benefit the powerful that they never explicitly asked or voted for, and that were never on any platform. Even whole wars can be promoted onto them...
https://www.smithsonianmag.com/history/posters-sold-world-wa...
Besides, there were tons of dirt poor whites picking cotton in the South. And they had no slaves, the were closer to slaves themselves...
It's more poor vs rich, than white vs black. Even if poor whites were also racist, those plantations weren't owned by poor white folk either...