Well, since most metal heads like to call Black Sabbath the first metal band, let's take them for instance. They had influences, right? Since they were the first metal band, their influences were not metal, right? That means Black Sabbath did not have metal influences. And therefore, a band
does not have to have metal influences in order to be metal.
Have you heard Opus Dei? I'm thinking no. Maybe you can list the metal bands that have influenced Rammstein, starting with the most influential. A band with 100% non-metal influences (such as Rammstein) isn't metal, even if they were for the sake of argument only 80% non-metal influenced they still wouldn't be considered metal. Why should they be?
Just out of curiosity, can you name me some metal bands that Ministry has cited as an influence? Because from my understanding, the vast majority of their influences are industrial, new wave, electronic music, etc. Not metal. And yet even the Rammstein naysayers here seem happy to call Ministry metal.
I can see Rammstein as having come from a primarily (non-metal) industrial base. However, since Rammstein utilises such heavy metal elements as loud, distorted guitars, chugging rhythms, heavy drumming, bombastic lyrical themes, etc., they sound like more than just their influences. Just because you can't point to "
the metal band" that influenced them does not mean that they hadn't heard metal before, and decided, "hey - let's mix some of that style with an industrial sound and do industrial metal!"