Good topic.
A syllogism:
If God is all-knowing, he knows about all evil.
If God is all powerful than he can stop all evil.
If God is maximally loving, he would want to stop all evil.
Evil exists.
Therefore a God who is all-knowing, all-powerful and/or all-loving does not exist.
The problem is that 2 and/or 3 aren’t necessarily true.
God cannot do illogical things (like make square circles or free robots). To have truly free humans existing, he can’t stop all evil.
Is it true that God would be unloving for allowing evil? A father who takes his kid to the dentist loves his child enough to allow pain for a greater good. So also, God may allow pain and suffering for a good reason.
This is the Christian story and I think it makes sense. So, yes, humans are responsible for evil because God can’t stop us without violating our free will or killing us all off.
See William Lane Craig’s work on the problem of evil. Here’s an intro: