It's actually very easy, because only one person is compiling 'official' bitcoin client which is used by thousands users, force this person to corrupt, backdoor 'official' client and you can destroy bitcoin in just few second... and don't give me argument you 'can Compile it yourself' 90% use standard bitcoin-qt client.
I compile from source. So I'm the only one in the world?
Fail.
Do you read source before compiling ? I used to but stopped when windows 95 was realeased.
Well no. But I sometimes look what changes have happened since last version.
You have to put some trust in at some stage. Be it hardware level, OS level or software level. There's no getting around it.
For example, do I check all the source code of Linux and compile it myself. Of course not. I take a leap of faith.