Your explicit statement is that I should not be allowed to prevent cats from roaming into my garden by personally discouraging them by whatever means I see fit at the split second I see them. As you seemed to imply your dog may prevent such a problem, you're knowingly leaving a dog that you openly admit may kill a cat somewhere where such an encounter may happen.
Basically, just like what was discussed earlier about it being ok for cats to kill birds, yet not for a human to inflict less lethal harm on cats to prevent them killing birds; you're now stating that it's not OK for me to kick a cat, yet it would be OK for me to buy a dog which might kill one.
If I were a cat, i'd consider being kicked and learning my lesson a much more favourable option than encountering your lurcher.
I'm sure you can now see why I appear confused – I am. On the one hand I can't kick a cat as that would be cruel, but on the other, I can leave a dog for which I have responsibility where it may kill a cat.
For the record, I have no argument with your dog seeing off a cat, in much the same way I was vaguely amused by the python. I simply can't understand why you're happy to leave your dog where it may kill a cat and not consider that outcome as cruel, whereas it seems I'm worse than a seal clubber if I were to merely kick a cat.