“The fact that you don't like slugs, mice and reptiles living in what is essentially their natural environment doesn't mean they should be killed there with salt.”
The point is that a patio is not a natural environment you have decided that when you laid the slabs, salt is not an approved weed killer, although on a patio is not going to cause a major problem. I don’t have any aversion to frogs and snakes etc, my garden is very dry year round so highly unlikely.
Glyphosate has been a generic chemical for many years mostly made in China these days and is very cheap, the only research in recent years has been done by environmental groups trying to rubbish it. First used in the mid 1960s it replaced many highly toxic residual chemicals, over 50 yrs on it’s probably the most widely used chemical worldwide and still very little evidence of any harmful effects.