I am not sure what this is seen as a terrible thing - it is referring to the invention of methylated spirits - a product still available today. The color and bitter additive WERE added to stop people drinking it - but it was not a conspiracy to kill people or anything as dramatic as that.
Also, not all countries use poison in their meths - NZ and Australia for example only added bitter flavor and color - making it safer to drink than the US counterpart.
The reason that this was done in the first place is because denatured alcohol is needed cheaply for a variety of non-drinking tasks such as cleaning, science, etc. By adding the dyes/poisons/flavors to it, the government doesn't need to tax it.