because it's far too easy for the bank to abuse.
It's not like you can't read the contract before you sign it. If you don't
like the terms, you can always refuse the loan.
That should not affect your rate.
Yes, it should. A longer time horizon for a loan means greater risk for
the lender. If rates go up in the future, the lender loses out on the greater
gains that could be made at the time. If rates go down (more than slightly),
the borrower refinances and the lender will have to reloan out the money at the
lower rate. Unexpected inflation will also cost the lender, and that's more
likely than deflation.
By letting the rate on the loan adjust, the lender can reduce the interest rate risk
for the loan. Reducing the risk allows them to offer a lower initial rate. If
you only expect to hold the loan during that initial rate period, an ARM will
probably be a good deal.
ARMs are for the bank's benefit, not yours. Unless you're a
banker, or can ONLY get an ARM, you're being screwed.
Nobody's ever going to force you to take an ARM. I'm looking for a house
right now that I fully expect to live in for no more than six years. If I
could get a 7/1 ARM with a lower rate than a 30-year fixed, I'd be a fool not
to take it. If there's a chance I'll still be in the same spot eight years
from now, then any motivation to get out is a good thing.
You're completely right that the banks are in business to make money, not to
be your friend. If they can't make money on a loan, they won't make the loan.
You can "convince" banks to make unprofitable loans with subsidies, ie FHA,
mortgage interest deduction, but since those are partially responsible for the
housing bubble, that tactic seems somewhat questionable.
Just because some unscrupulous lenders push specialized loans onto people
who shouldn't really be using them doesn't mean that there aren't valid uses
for those products, though. As long as you pay attention to what you're
signing, the banks can't screw you without saying so first.