I think they're great questions! I would take them seriously regardless of who is asking.
First, hopefully you noticed I was speaking generally about the "unholy". In particular, it's a case by case evaluation, and holy/mundane/unholy is a spiritual quality so, a person is looking for signs to indicate what it is. That's why I said "generally your excrement is unholy".
Regarding animals, insects, humans, plants, rocks, whomever, whatever, unholiness is not transferred in that way. A person doesn't become unholy, if they are in a situation where they need to consume something.. rotting, decomposing. There's stories of captured soldiers being tortured and being fed a "bitter meal". Not sure if the stories are true, but, this in no way makes the soldier unholy. The pet consuming its own feces does not make it unholy. The dog drinking from the toilet, the flies in the garbage... doesn't change them that way.
In general, animals, plants, insects are less sensitive than humans in a lot of ways. They are canabalistic, they have no qualms killing brutally. Plants will mercilessly take over a yard killing the other plants, and knock down a house by invading the foundation, etc. But they are also less sensitive to ecoli, and salmonella, and other harmful "stuff" than humans. So this insensitivity is not a flaw. It just is. And this doesn't in any way detract from their positive qualities. I love animals and plants. In a way, I think they are capable of love as well. I even love insects. I have an affinity for ants and ticks, believe it or not.
One of the ways they are insensitive is they are lacking an aversion to things that are unholy. Again, in general. This, imo, is by design. They are part of the cycle of life. When a fly is feeding off excrement, it is further seperating and sifting out the 'husks' 'shells' 'peels' of unholiness from the 'leavings'. In this way, true, the 'leavings' are not completely unholy when they 'leave' the human body. There is still something nutritious there which can be sifted further from the 'dross'. They are able to sift it and sort it further than a human as a result of their insensitivity. They are like nature's refineries.
And this is why it appears as if unholiness is relative. The vast majority, almost everything that exists is a mixture of holy/unholy. Again, it gets complicated. It's not that the excrement is unholy for us and not unholy for the animals, plants, insects, rocks, etc... it's that excrement is still a mixture of holy/unholy when it leaves the body, but it is much-much more unholy than holy. And the animals, plants, insects, rocks, etc are not naturally disinclined towards that high concentration so that they can fulfiill their function in the cycle of life.