I am pretty narrow-minded in what I consider a kilt.
According to dictionary.com a kilt is "A knee-length skirt with deep pleats, usually of a tartan wool, worn as part of the dress for men in the Scottish Highlands."
Although it does say "usually" of tartan wool, but to me, if it isn't made of wool... then it really isn't a kilt.
I know most of the people on this forum wear kilts that are made of other fabrics, and that is great if that is what you want to wear.
However, personally if someone makes any comments about what I am wearing I want to be able to tell them "this is a kilt, not a skirt." In order to feel that I am right when I say that, there needs to be a clear line in my mind between what is a kilt and what is a skirt. So to me a kilt needs to be made of tartan wool, and sewn in the traditional way.
Also, being in Japan I want to be able to explain to people that it is a traditional Scottish garment, and I couldn't say that about a kilt that wasn't made of wool without feeling that I was lying.