SATANISM

[MR. Macabre 666]

Because there are dozen's of other bands that are better, heavier, darker, and more authentic than any band who's shirts you can buy at Hot Topic. I've been listening to black/death metal for over 20 years, and "traditional" metal bands for over 20 years before that.
Whitechapel is a metal band?
If you're interested in hearing some real music, try this short list and let me know what you think,
Emperor
Immortal
Watain
Behemoth
Inquisition
Dark Funeral
Batushka
Hypocrisy
Morbid Angel
Dimmu Borgir
This would be a good start.

Went by my cousin today. Listened to Dimmu Borgir for the 1st time. I LOVED them. It was their album Death Cult Armageddon. He had a signed copy (CD) and he also got the Deluxe Edition CD from the collection he bought so he gave me it.

Genuine question here, I'm not trying to accuse anyone:

To what extent to bands like this use Nazi or White Supremacist imagery? 

I know that some people who don't believe in a real Satan use Satanic symbols (partly) for their shock value. It's fun to get a rise out of little old ladies. 

Is Nazi stuff used for the same purpose, even if people don't particularly believe it?

Most don't, some use it for shock others deface it, like Pantera always has a ruined confedrate flag in allot of album/shirt art. But like every community there is always gonna be that 1% that is racist/sexist/homophobic that no one in the communites like.

Check out their earlier records, you might like those even more. Spiritual Black Dimensions, Enthrone Darkness Triumphant, and Puritanical Euphoric Misanthropia are all awesome records.