Why is it dangerous to pet stray dogs?

Everyone was told in childhood that stroking dangerous dogs is very dangerous.
Firstly, this is because they can bite, no one knows what exactly is on her mind, and suddenly she is sick with rabies, it will have to do a bunch of injections and go to hospitals.
Secondly, stray dogs often have diseases, because no one cares for them. You cannot know in advance who touched her before, where she was. And when you stroke her, the whole infection remains on your hands, and there is a high probability of getting infected with something, because by stroking a dog on the street you will not be able to wash your hands right away. In such cases, you need to carry wet wipes with you or it is better not to iron at all.