Well, there's really no debate about the not necessary part. The AC power adapters for almost all modern electronic appliances are auto switching, so all that's needed is a proper plug adapter. Personally, I've traveled from the through Europe, Africa, etc., with phone, computer, razor, etc., and never needed a converter.
The 'bad idea' part is more debatable, true. First off, if you don't need it, why use it? Second, quality and condition of the converter are a factor - low quality units (or higher quality ones previously damaged by surges) produce inconsistent voltage fluctuations, which can lead to excess heat in the converter and in the AC adapter connected to it. Also, as noted on the site you link, converters are generally not rated for continuous use. Some of the transformers (at the bottom of the page you link) are rated for that.
You also mention use with 'other appliances' - personally, my wife has 2000 W hair dryers and curling irons, either of which exceeds the capacity of a typical converter. Instead, we typically purchase inexpensive 'local' hair dryer for use while we're there, and give them away when we leave (only if needed - when in nice hotels in Europe, they are provided, but not, for example, in small towns in Rwanda - but there, the problem is not availability of appliances or whether or not you have a converter, it's whether or not there's electricity at all, or even running water 😉 ).
