don't need to trust core developers
> It is easy to destroy the bitcoin if I am the core developer.
Show me the kill switch (source). Fact is that there is none. So you are wrong.
This will be my last answer, I'm not losing time if you don't want to learn anything from what we reply to you.
You are perfectly free* not to trust Bitcoin and never touch it again.
* freedom comes at a price
If I have that "key" to broadcast the "upgrading" message(the core developer has the key), too many clients will be upgraded to a Trojan software. The software will send the private key to me continuously. Then the bitcoin network is destroyed. It that simple?