You can't really discuss these kind of questions without concrete variations. But let us try.
The early move e6 in Colle is not played to defend d5, but to defend c5 + take space in the centre and develop Bf8. But is blocks Bc8. The alternatives will have to be a delayed e6 (allowing Bc8 to develop to eg. g4) or g6 + Bg7.
Normally White is not afraid of c5xd4 as e3xd4 is the kind of attacking positions you are heading for (Bc1 is now un-blocked). If the Nb1 is still in the starting position White can also play c3xd4 + Nc3 with initiative in a symmetrical position.
In the main line setup, black plays ...e6 before or after ...c5. I dont understand why playing ...e6 as long as white didnt play c4 ? It allows recapture the pawn after dxc4, but wouldnt it be better for black to play ...cxd4 before white plays c3 ?