[lYVgWWcP]

When a sense organ makes contact with an object something we call ego immediately reacts to this contact in some way

This statement pre-supposes the constant and continuous existence of some "thing" that "we call ego" that generates attraction and aversion to sensory data. It is a doctrine of "Attavada".

Nothing intrinsically wrong with such a hypothesis, but the Buddha taught something vastly different.

this plants a seed in the consciousness, which when watered by repeated ego responses will bear fruit or have an effect.

Now we have two Attas at work here -- a constant and continuous ego, and a constant and continuous consciousness. Neither comports with the Buddha's doctrine of Anatta. The Buddha taught vinnana, which we translate as "consciousness", as a process of awareness of a sense object through a sensory system, and nothing more. This awareness comes and goes as sense objects enter and leave the range of that sensory system's capabilities.

Vinnana for the Buddha was not some cosmic karma repository.

...further down the line in the stream of consciousness

The idea of a "stream of consciousness" is a much later invention. Again, for the Buddha, vinanna is not a constant and continuous "stream", but one of several perceptive processes that arise and disappear completely according to contact that arises between a particular sensory system and objects that fall within that particular system's sensory range.

If one believes that the mind does not depend on the body for existence it is easy to see how holding such a powerful belief (of harm coming from without) could lead to an existence in a hell realm.

A person who commits a premeditated murder believes that there will be no adverse consequences. And believes powerfully enough to carry through that intention of premeditated murder. Otherwise, that person would not commit a premeditated murder. Holding such a powerful belief, of no harm coming from without, how could a hell realm come to be after death, through the mechanism of that person's "strong belief", for that person in the speculative scenario you suggest?

I personally do not believe that the mind is dependent on the body for its existence, but if someone else does, this reasoning would not be helpful.

Nor would it be helpful or relevant for one who does not hold a belief that the mind can exist separately from the body, meaning, neither claims that "the mind is separate from the body", nor claims that "the mind is not separate from the body".

The Buddha did not hold that the mind exists separately from the body, by the way.

Also, I wonder sometimes that when we lash out and attack another are we not really attacking our unconscious projections.

I think that we are attacking both unconscious and (even more so) conscious projections. We actively ignore any good qualities a person might have, and hold to any detrimental ones we might conceive as we formulate our aversive intentions.

in our mindstream

Again, a constant and continuous "mindstream" is an attavada notion the Buddha did not teach.