Poisons are widely available to everyone. People commonly have liters of them under their kitchen sink or in their garage. Many of them are also simple compounds that anyone can make, e.g. "cyanide" is just CN (carbon and nitrogen) typically attached to H, Na or K. Every one of those elements is required for human life, but combining them in specific ratios under well-known conditions creates a deadly poison. It's so simple to do that hobbyist chemists have to be careful not to create it by accident.

> But I am concerned that this will be worse than a more broadly trusted image environment

There are two different metrics of trust here.

The first is, should you trust an unauthenticated image you see on the internet? Now more than ever before, the answer to that question is no. Watermarks can't fix that because the people you least want to be trusting are the ones who can still forge images without any watermarks. You can't undo this by putting watermarks on other images.

The second is, do people trust random images from strangers on the internet? The ostensible purpose of doing watermarks is to get more people to do that. But when the answer to the first question is no, getting more people to do that is bad, because you're encouraging people to trust something that is not trustworthy.

What you want is for undetectable forgeries to be difficult/impossible in general, e.g. to have something that can tell anyone if an image is machine-generated regardless of whether the machine added a watermark. But watermarks don't give you that since they don't all add them or can feasibly be removed, and a generic algorithm that can detect even novel/unknown image generation methods may not even be possible.