Why were the words with silent letter (unpronounced) made? Isn't it
confusing and unwanted?

Yes.  The Brits, and we Americans (along with the Aussies and Kiwis)
have conspired to make sure we can easily pick out foreigners in a
crowd by their mispronunciations.

BBC
http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv205.shtml

Let me know if this answers your question.

tutuzdad-ga

The history of English spelling is fascinating.  I'm sure a researcher
could recommend books on it.  Here's one brief link:
http://www.newsandevents.utoronto.ca/bios/askus32.htm

The words you use as examples all eventually derive from Greek, so the
spelling was likely influenced by the Greek origin.  I doubt that the
silent letters were ever pronounced.  However, other words have silent
letters that used to be pronounced.  For example, "knife" used to
sound something like k-nee-fuh.

Sometimes extra letters were addded to words for decoration or to make
them look more like Latin (back when Latin was considered the ultimate
in languages).  When this occurred, an amusing phenomenon called
"spelling pronunciation" could follow.  Spelling pronunciation is
pronouncing a word according to its spelling rather than how it has
traditionally been pronounced.  (
http://en.wikipedia.org/wiki/Spelling_pronunciation )  For example,
the "g" in the suffix "-ing" was added for decoration.  Initially it
wasn't pronounced at all.  "Spinning" used to rhyme with "linen." 
However, people eventually felt compelled to start pronouncing the "g"
somehow, so the "ing" sound you know today was evolved.  I think this
occurred in England but not Scotland.  Some of the American accents
that don't use the "ing" sound (e.g., helpin' instead of helping) have
not corrupted standard American English--they derive directly from
variants of British Isles English that didn't use "ing" either.

I'm not a researcher; this is a free comment.  Source:  stuff I
vaguely remember from a class I took last year.

As biophysicist says, a fascinating subject.
A good (non academic) reference book about the development of the
English language I can recommend is Mother Tongue by Bill Bryson.
(http://www.amazon.co.uk/exec/obidos/ASIN/014014305X)

This covers the various influences, espcially the divergence of
British English and American English, and makes a good read too!