The idea of e6 is not just to block the bishop, it's also to play an early d5, which just happens to hit the bishop on c4. This is another reason it's badly placed there, don't forget the fork trick also.
It may be a bit much to call 2.Bc4 a sin that must be punished, but it is kind of sad that people play it considering that those who want to avoid Sicilian theory have so many interesting anti-Sicilian options to choose from (The Sicilian having far more "antis" than any other response to 1.e4), but instead of selecting from this array of options these people just play 2.Bc4. It's kind of like taking someone to a luxury clothing store and saying "you can select anything in this store that you want", and they go "no I don't want to pick anything out here, Instead I'll just wear this dookie-stained shirt I got out of a garbage can". 2.Bc4 is playable, just as a dookie-stained shirt is wearable, but in both cases doing so sends the message that you're lazy, apathetic, and have no real interest in chess or anything else.
By the way, Rybka 4 says 2...Nc6 is stronger than 2...e6. I have tried various set-ups against 2.Bc4 and I do have the most success with 2...Nc6, because it's best to develop some pieces before breaking in the center with an immediate e6-d5. After 2...Nc6 White should bring one of their knights out then Black plays 3...Nf6 There are some slighty tactical variations involving early e5 pushes (or counterpushes in response to Black's d5), and also one where White sacs a bishop on f7, but they all work out for Black.
I have seen many engines give 2.e6 as the best.
The idea of e6 is not just to block the bishop, it's also to play an early d5, which just happens to hit the bishop on c4. This is another reason it's badly placed there, don't forget the fork trick also.
It may be a bit much to call 2.Bc4 a sin that must be punished, but it is kind of sad that people play it considering that those who want to avoid Sicilian theory have so many interesting anti-Sicilian options to choose from (The Sicilian having far more "antis" than any other response to 1.e4), but instead of selecting from this array of options these people just play 2.Bc4. It's kind of like taking someone to a luxury clothing store and saying "you can select anything in this store that you want", and they go "no I don't want to pick anything out here, Instead I'll just wear this dookie-stained shirt I got out of a garbage can". 2.Bc4 is playable, just as a dookie-stained shirt is wearable, but in both cases doing so sends the message that you're lazy, apathetic, and have no real interest in chess or anything else.
By the way, Rybka 4 says 2...Nc6 is stronger than 2...e6. I have tried various set-ups against 2.Bc4 and I do have the most success with 2...Nc6, because it's best to develop some pieces before breaking in the center with an immediate e6-d5. After 2...Nc6 White should bring one of their knights out then Black plays 3...Nf6 There are some slighty tactical variations involving early e5 pushes (or counterpushes in response to Black's d5), and also one where White sacs a bishop on f7, but they all work out for Black.