> if an ad is straight facts
How would you determine this? Distinguishing fact from opinion is impossibly difficult, just ask social media companies.
Besides, ads are supposed to be manipulative, otherwise they wouldn't be nearly as effective. Taken to its extreme, and with the capabilities of adtech, it's no wonder they're used for propaganda, to influence elections, etc. None of this spreads "new information" meant to educate people, but mostly falsehoods with a specific agenda from anyone willing to pay for it.
In addition to being impossible to determine what constitutes as propaganda or not, fact-checking ads would go against their whole purpose, against all the "progress" the advertising industry has made in the past century, and would crumble the current adtech giants. Hell freezing over has better chances of happening.
> More philosophically, should we, as free-willed people, be prevented from seeing "untruths"?
If those "untruths" are used to psychologically manipulate people to get them to buy, vote or think a certain way, then I'd argue that they're doing a net harm to society, and should be heavily regulated.
We can't control and fact-check speech, but we can limit its spread. What the internet has allowed is an unprecedented way of spreading information, and we can certainly control that. The difficult thing is again, determining what is "harmful" or not.