The problem is that people that know a bit about the internal construction of batteries have often worked on safety too. I have done what we called "abusive tests" for 3 years on Lithium-Ion cells, finding all possible ways things could go badly, and this kind of work tends to make you paranoid
In addition the battery has a strong case with blow off vents to release excessive pressure.
Yes that's true. Often when there is excessive pressure there is also a thermal runaway going on and it's not just gas that comes out, it's a flame that can be 10 times longer than the cell itself.
I know that I sound "end of the world" but when you are working on something that can potentially burn your house down, take a few precautions. Protection circuits for Li-Ion are dead cheap, there is no reason for not using them, at least for charging. Please use them. Thermal runaway on a Li-Ion cell can start at a voltage as low as 4.35V, all it needs is a badly calibrated power supply.