[foldr]

As has been repeatedly said, the problem is that small balls of solder can persist in your home environment, which makes it difficult to be sure that you’re not eventually eating them. For example, solder balls caught in your clothes or hair can fall off and land in food or drink that you’re preparing. It’s very difficult to quantify how likely this is to happen, but it’s not that outlandish of a possibility.

Now of course you could be really careful about changing your clothes and washing after you solder. Then again, you could also just use lead free solder, which works fine.

[CamperBob2]

Or you could cite some reproducible statistics indicating that this actually happens in real life, in quantities that affect human health and development rather than mass-spectrometry plots.

Fact is, there was never any actual science behind the RoHS prohibition of lead solder. Not while lead-acid battery production was still permitted, certainly. The same people who thought it was a good idea to do this also thought it was a good idea to shut down all the nuclear plants in Germany because of something that happened at an unrelated facility in Japan. We're not allowed to argue with them because reasons.

[foldr]

We are not discussing the question of whether leaded solder should be banned, but the question of whether it is advisable for hobbyists to use it in a home environment. RoHS prohibitions on leaded solder have nothing to do with concerns about the safety of home soldering.

I'm not sure why you think that the absence of relevant safety data argues in favor of using leaded solder for home soldering. Surely one should err on the side of caution. I use unleaded solder myself without problems. Why then would I want to take on the additional risk of using leaded solder? It's worth noting that there is no known safe dose of lead ("there is no lower threshold to the dose-response relationship below which lead exposure is treated as safe" [1]). If you are spraying little balls of lead around your home environment, it's obvious that there is a non-zero risk of eventually ingesting some of them. People aren't doing scientific studies to prove that because it comes under the heading of the "bleedin' obvious" :)

Of course everyone can make their own decisions here. If you really want to use leaded solder then go ahead. What I don't quite understand is why some people react so strongly to the precautionary advice to use unleaded solder.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4961898/