Did you know there are people who refuse to learn to read because they feel it degrades memory? I always think of that when I hear arguments like this.

Old people have been saying that about all technology since the beginning of recorded history. it just means that people don't stay exactly the same as they have always been. Novels were mocked as being foolish, books themselves were mocked when they replaced tablets, i mean it goes on and on. And you're right that abilities may atrophy. Do people have poorer handwriting now? Yes. Does it matter at all? Not really. I think you're wrong though about memory atrophying. I have been using computers and cell phones since I was a child, and I have excellent memory. Regarding navigation via phone - Can I conduct orienteering with a map? No. Does it matter at all? Not really.