I was actually already into both clean and harsh vocals before I got into Opeth. \()/
I don't really see the problem with HD only liking those types of vocals. They certainly take talent and can sound much more interesting than a usual voice on occasion.
Go ahead and enjoy all the "clean vocal" songs, but I promise you'll be hooked to the "harsh vocal" ones in no time. Their music is just too good to be skipped.