can you expound this proverb "a thief thinks everybody steals"?

.... and the saint sees God in everyone.

There is no "honor" among thieves,

liars, the arrogant, greedy.

The opposite is not true.

A generous kind "humanitarian" knows of all those above,

and still tries to help them.

People rationalize that others are like them and therefor they are just as good as others. Yes it does apply to other vices. A person naturally wants to feel good about himself. They know that everybody has flaws and so they rationalize that there are enough people doing exactly what they are doing that it makes their crime normal.

It is a flawed argument against strict moral behavior suggesting everyone does it so it is ok. We see this kind of thinking in a great deal of political rhetoric.

I think it means that a thief judges every one by his own standards, Or to justify his being a thief.

Yes I think to some extent it applies to the others you mention. But not those who do good, because they don't have an axe to grind.

People assume that others are like they are. The thief assumes everyone steals, the murderer lives in fear he will be murdered, the generous and kind are shocked by the world today.

Making common assumptions can have serious consequences, including weakening your position, inadvertently encouraging highly competitive behavior, and misreading others' actions.

All the events are revealed to a person because of his incomplete perception because of his uncorrected sensations. The world is depicted as incomplete according to a person’s perception and understanding. But we should understand that this imperfection is not in the external world, but in ourselves.

http://laitman.com/2012/08/my-evil-under-a-620-tim...

http://laitman.com/talks-about-a-new-life-episode-...

People whom cheat on their spouse tend to fear that their spouse may be cheating on them. Many habitual liars tend to think that everyone lies so they are just doing what is normal.

Some proverbs ring true, while others are just food for thought.

http://www.historyofpainters.com/india_proverbs.ht...

It means a person thinks everyone (is, feels, thinks) just like they do.

What? Besides the fact that it's utterly incorrect? No, I cant "expound" on it.