Silent Letters?

I don't know if this idea bothers anybody else, but isn't silent letter an oxymoron? It seems to me a letter is a symbol used to represent a sound. I suppose some letters help us pronounce another letter--like the "e" helps us distinguish between hat and hate. Still, English seems to me to have an over-abundance of silent letters, most of which seem completely superfluous.

Every letter in the English alphabet is silent in at least one word. Check it out:

read
debt
science
Wednesday
life
buff
high
honor
business
hajj
knife
talk
mnemonic
hymn
opossum
psychic
lacquer
myrrh
island
listen
guest
revving
wrong
faux
they're
rendezvous