Also, your understanding of chirality is confused. The D-form and L-form notation of amino acids does not refer to the direction in which they rotate a plane of polarized light, but to their structural similarity to the optically active enantiomer of glyceraldehyde which does. For example, an amino acid may technically rotate a plane of polarized light to the right [and be dextrorotary, more properly notated (+)] BUT still be the L-form if it is structurally similar to levorotary (-) glyceraldehyde that rotates a plane of polarized light counter-clockwise, to the left.

I would also like to point out that the existence of naturally-occurring racemic mixes (50:50) of amino acids would not prove anything. To the best of my knowledge, it is believed that once L-amino acids began to be used biologically, everything else after that could only work with that, and so it did. It could have just as easily been the other way around. The fact that the overwhelming disparity exists rather than different phyla or whatever using their own form is actually very good evidence for common descent (i.e., evolution). This statement

“If even very small amounts of amino acid molecules of the dextrorotary
type are present, proteins of a different 3-D structure are formed; these
proteins are not capable of supporting life, and often can be fatal to life.”

is simply not true. The incorrect enantiomer would not be incorporated into a protein at all–most likely it would harnlessly excreted–or it may in fact be switched to the “correct” form by a racemase enzyme.

And finally, D-forms of amino acids are not necessarily not physiologically active. D-amino acids are incorporated into peptidoglycan in some bacterial cell walls. A more relevant example: D-serine formed by serine racemase activates NDMA receptors in the brain and is being investigated as an important neurotransmitter.

What was the chirality ratio of the glycine amino acid molecules found in a sample returned by the space probe? Was it 100% laevorotary (as required by living organisms), or a 50:50 mix, as occurs with lab experiments on Earth?