"If God doesn't exist, everything is permitted."?

Despite my disbelieve in the existence of a rewarding and punishing God I prefer to be "moral" and "ethical." How do you explain that?

I'm not sure to whom your question is addressed JLN but there are several levels of "explanation" which need not be mutually exclusive.

1. Concepts of "God" are predicated on concepts of "morality", not vice versa and constitute the simplistic personification of a social regulatory authority.
2. "Morality" is an evolutionary trait transmitted genetically assisting mutual group survival.
3, Concepts of "self" are socially acquired via a common language involving "actors". The "self" is predicated on its relationship to others. Selves are "moral" because psychologically they need to live with "themselves" in one's thoughts.

Unless we follow Kant who argues for universal "moral imperatives" (such as never telling lies) it follows that morality and ethics are embedded in the language which is our vehicle for "thought". And since languages differ we can expect that concepts of morality will differ accordingly. Consider for example the idiolect of an underclass which allocates the nebulous term "them" to "the rich". This psychologically places "them" in an out-group relative to which in-group principles of morality need not apply. Thus stealing from "them" need not be deemed "immoral" whereas informing on in-group perpetrators is. And by extrapolation we can easily arrive at explanations for terms like "a just war".

A lot of nominal christians ignore this passage in Romans:Clear evidence that Christians have no exclusive on morality.

No matter how "nice" and "decent" an atheist may be, can they really be a truly moral person if they reject Jesus and go around attacking him and Christianity?

Of course they can if "belief in Christ" to them means advocating an authoritarian stance on morality coupled with the promise that submission is the only root into a mythical afterlife. Christians like you, who may be apologists for the "nicer side" of Christianity may be seen by atheists, as giving succour to their more zealous fundamentalist brethren who tend to impede individual rights. Every time you resort to "holy writ" in defense of Christianity, an atheist will merely role his eyes at your appeal to a synthetic authority which is no different to a fundamentalist tactic.

Jesus said -"For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life" (John 3:16)
"For I didn't come to judge the world, but to save it" (John 3:16, John 12:47)

which gives rise to the question- if an atheist is a nice person but pooh-poohs Jesus, will he/she still be saved?

Saved from "what" ? ....devils, ghoulies, pain ? ....to get what? ....perpetual ecstasy ?...very tiring !
Don't you understand what I just said ? You just shot yourself in the foot by your appeal to "holy writ".
Atheists have no doubt that such texts have been selected and composed by both well intentioned and politically aware individuals seeking to justify their own existence and position.

We're all in a totally crazy situation trapped in these squishy fleshy bodies on a spinning ball of mud that's sailing through space, without knowing how we got here or where we're going when our bodies die.
So when Jesus says "I'll tell you things hidden since the creation of the world" (Matt 13:35), isn't it only logical that we should listen to what he has to say?
How about you Spock?

"Affirmative, I'm all ears"

No. Its as logical as listening to any other religious orator who thinks he knows what he is talking about, including " mad mullahs".
You are under the medieval assumption that you have a self/soul "trapped in a body". As long as you realise there is zero evidence for that view you will be stuck with the fairy stories that rationalise that view.
If you are looking for " logic" , I suggest to you that Marx was spot on with comments about religion being the opium of the masses.

Not a medieval assumption, much older, but false nevertheless.
He did not get that from the Bible, BTW.

Point taken. I was looking for an adjective other than "antediluvian" (which assumes the flood myth). I suppose the ancient Egyptians had a "soul story" for the pharaohs at least.

We may assume antediluvian belief to also have postulated a disembodied soul, as an answer to the delusion perpetrated by the serpent in Genesis Ch 3. "You positively will not die." Once folks started croaking, someone had to advance an explanation. And, indeed, the Greek/Roman religions (which remarkably reflect the asserted Noachian era) seem to verify this.

A thought occurs: If a G*d has given beings of his own creation 'free will' isn't "everything is permitted" what we have today?

Romeo, you ask "if an atheist is a nice person but pooh-poohs Jesus, will he/she still be saved?" I cannot discuss the idea of being saved, that's too absurd for serious thought. But let me note in passing that I was not pooh-poohing the historical Jesus only the idea of the Christ, and that is a creation of men (Paul in particular).

Everything tolerated, yes.
For a time.

Guys guys, Jesus said we have a soul/spirit/life force, so who shall we believe, him or you?
Jesus said-
"The spirit within gives life, the flesh alone is worthless" (John 6:63 )
"What good will it be for someone to gain the whole world, yet forfeit their soul?" (Matt 16:26)
"Love the Lord your God with all your heart and with all your soul and with all your mind." (Matt 22:37)
"..this night thy soul shall be required of thee" (Luke 12:20)
“My soul is overwhelmed with sorrow to the point of death” (Mark 14:34)
"Father into your hands I commit my spirit" (Luke 23:46)

There is a difference between soul and spirit. That's why they used different words.

The words soul and spirit are interchangeable depending on context, and basically mean "life force".
For example when Jesus said "Father into your hands I commit my spirit" (Luke 23:46)
he meant his "life force" of spirit and soul combined.
If spirit and soul are separate things, that'd mean his spirit flew but his soul stayed behind, a crazy notion..

His soul died
His spirit had no life of its own.

Jesus often spoke of eternal life, so I think I prefer to believe him rather than you and your JW chums..