Daniel brings up an interesting point, that includes several issues. First, to what extent is it necessary or desirable to obtain the very best ingredients for a given recipe? Is it ever acceptable to go with a substitute - like bottled juice instead of fresh?

Second, is it ever desirable to change an authentic recipe to "improve" it? Check out this history of Key lime pie. If this is true, we have to accept sweetened, condensed milk as a valid, authentic ingredient. If canned milk is acceptable, why isn't bottled juice?

I bring this up to get a discussion going. FWIW, my opinion is 1: go with what tastes best, and 2: if you can't tell the difference, go with what's most expedient.

I did a side-by-side in DC once of key limes from Whole Foods, the bottled stuff, and Persian limes. All had a shortbread crust, whipped cream and not meringue on top, and a cooked filling. Hands down, the Persian limes won. The others had an off taste.

I then did a side-by-side in Big Pine Key of key limes off the tree in the backyard and Persian limes. Same treatment as above. Hands down the key limes won. They were lime-ier. Since then I've slightly increased the lime juice and barely sweeten the whipped cream to try and replicate.

There is no question that fresh trumps pre-made, bottled or canned as regards the lime juice, and also the crust. I was merely making the point that it is possible to make a perfectly acceptable pie, as good as or better than most commercially made key lime pies, with very little time and effort. You could make a better pie by squeezing limes for fresh juice (Persian limes will be a little bit less acidic) and making a crumb crust from scratch--especially if some ground nuts are included in with the crumbs and butter. That will take a considerably greater investment of time, however.

As regards the question of sweetened condensed milk: I believe that the recipe was developed using this ingredient, and I doubt that the desired end product would be effected if it weren't used. You might make a different sort of lime pie--like lime chiffon, or a lime meringue pie without sweetened condensed milk. But the obvious question is--what's wrong with using sweetened condensed milk?

The more obvious question is--is it better to sweeten and condense your own?