This was the reason for my admonition. Even the manufacturers of sweetened condensed milk had advised against this process as other options have evolved. If the water level isn't right, if the can has an unseen defect, if it's forgotten on the stove, etc., there can be problems. The other methods have fewer risks.
This is directly from the Eagle Brand website's FAQ:
Is it safe to boil my can of Eagle Brand Sweetened Condensed Milk to make caramel sauce?
No. For safety reasons, we do not recommend heating a can, opened or unopened, of Eagle Brand Sweetened Condensed Milk. The current can is not designed to withstand high temperatures. Instead, please follow these instructions for making Homemade Caramel.