Worst blackjack player you've ever seen?

[playersare]

doubling 7 on ANY dealer upcard using ANY number of decks is not profitable. a starting hand of hard 7 in any blackjack game is extremely marginal, and doubling (regardless of upcard or table conditions) would be solidly -EV in the long run.

however, I did have to look at the charts in BJA3 to confirm this, so I admit your theory seemed somewhat intuitive to start. unfortunately, it doesn't hold up.