Innocent until proven guilty is a relative term. Presumption of innocence must also be
balanced in accordance with public safety. The reason it is done this way is because
we do not want to lose the presumption of innocence or we end up with people in the
prisons for other reasons, like political reasons, or because they are a pain in the a**
without a reasonable expectation that they were actually guilty of the crime they were
supposed to have committed.
As for bail, in most cases bail is granted due to the fact the courts take a long time to
go through the system and people waiting for trial for relatively small offences should
not have to be in prison in cases like that. It is called reasonable compromise and is a
useful tool. You are right though people like Pickton and others, do not get bail because
the offence is serious, and they are very likely to re-offend should they be on the street.
Innocent until proven guilty is a safeguard that protects the majority and as I said its a
reasonable compromise in the evolution of the system of justice. Besides this is Canada
it doesn't have to make sense.