That's phrasing it in a way that makes it misleadingly clear who's in the wrong: of course all good people will not want something like that to happen.
The devil is in the details. How much does that "illegal and harmful" content help their bottom line? Is it making 50% of their income? 10%? 1% or less? After knowing the percentage value can you still make a general statement like "companies are profiting on illegal and harmful content"? Or the more correct statement would be "companies make extremely little profit on illegal and harmful content"?
On the other hand, before proposing mandatory moderation for all user content on all platforms we have to ask more questions. How much would it cost if all content is moderated in order to catch that X% that is "illegal and harmful"?
Everything has a price.
The problem is that nobody actually has that data (and they'll claim your point is invalid unless you have the data, which only they even have the potential to gather). Google and Facebook will tell you it's very low, but since they're ignoring reports of malicious apps on their platforms and restoring scammy ad campaigns after they've been reported and taken down internally, what they consider bad content is likely much smaller than reality.
Honestly, with both the amount of flagrantly malicious content I see on Google and Facebook ad platforms, and the network effects that their participation has on bidding for placement, I would suspect that these companies are nearly dependent on malicious content for profitability.
Another huge point is that a lot of legitimate advertisers are paying just to protect their brand from having scams placed above their own site in searches for their trademark. This is pretty close to an extortion racket.
I think there’s a Big Short level event on the horizon where we discover some of the top valued companies on the planet are built on a lot more of this than they’ve let on.
When Facebook promotes falsehoods, they profit. When Google sells links to malware and scam sites at the top of search, they profit. And even if they get around to moderating these abuses of their platforms, they keep the profit from the harm done via their platforms.
If we want platforms to have the proper incentives to moderate content properly, they need to lose money when they fail, or at least, fail to profit when they fail. Ad money for malware campaigns and scams should be confiscated.
But right now, malicious actors on ad platforms drive up the revenue on bidding-based platforms, and no matter who wins the bid, that equals money for ad companies. They have fundamentally no incentive to police content that's making them money.