Here I'm concerned with the "opposite style" to a table of tight cash game players.

I first read of playing "opposite style" 10 years ago in "Harrington on Hold'em Tournament Edition Vol 1". Ok it's a tournament book, not cash.

But on pg. 46 at the top, he admitted there's "surprisingly little you can do" to defend against tight conservative players when blinds are small relative to stacks (e.g., cash games).

But my point: somewhere I read that a "loose" strategy is effective against "tight" players. But how can playing loose possibly be effective/profitable against tight cash players?
- Preflop: I assume it means upping your blind steal frequency
- Postflop: Is it because you get much more postflop play with speculative-hands than the tight players? Even factoring in implied-odds, I'm really really skeptical that this allows you to outplay your tight opponents.

Can anyone clarify this? Is it a myth? Thanks.

If tight players are yet to act, you can enter the pot before them with a steal attempt, expecting them to fold. (e.g. If you are on the button and both blinds are very nitty, you can steal with any two cards). If a tight player opens, you should duck out most of the time, because he'll have a real hand.
By playing looser than the nits, you'll make money by picking up dead money (from blind steals), but it will be a very dull game with mostly small pots. It's more fun and more profitable to be on a loose table where you are the tight player, because then you tend to have the best hand if you see a flop, so you can win some big pots.

Thanks for the great answer: try to steal from tight players yet to act, but tend to escape if a tight player opens before you (i.e., the Gap Concept). This question has been on my mind for years.

Pretty much what Arty said. Your value is going to come from by making them fold their equity pf by raising. In the low stakes live world, very few players are actually tight. Most are loose passive. Therefore, tight aggressive is going to when the money.