Well, my definition of "too many" has gone up and down the scales repeatedly over the last few years. At times I had over a hundred and it didn't feel like too many. Now I have (including the three that are supposedly on the way) ten decks and it feels like too many; five would feel more comfortable.
For me it's a matter of trying to be practical. I am trying very hard NOT to collect anymore. I want decks I will use, each of which offers something different enough that it doesn't feel like repeating, like I have clones or cookie-cutter decks. Do I feel guilty? Sometimes. Stupid, I know, but I do. I'm trying to simplify - the rest of my life is complex and cluttered enough!
ETA: I liked the "scorched earth" analogy. THAT is what my desire to cull down to five decks is about! By shaving the collection down to the bare bones, it is no longer a collection. Five working decks do not a collection make. And if it's not a collection, then I don't need to collect more! Or buy more!