As a beginner I face contradiction In fiancetto bishop openings

In the openings, I've been facing an issue. 
After my bishops are fiancettoed, why the positions arise where I must play move like e5 (as black), often times I get overwhelmed in the hypermodern openings and for this reason I feel bad playing kings indian or pirc defense.

often times I find that the dark square bishop is either trapped or traded.. 

My question is ... 
if you have fiancetto bishop on g7 Should you never! play e5? 
but if you must play e5 then the dark squared bishop is just trapped there.. due to usually white pawn being on e4. 
someone help

Having a Bishop trapped behind your own Pawns IN AN OPEN POSITION is bad.

Having a Bishop trapped behind your own Pawns IN A CLOSED POSITION is normal and good.

Here is Bobby Fischer playing a King's Indian Defense against one of the best players in the world (at the time).

@1

"the dark square bishop is either trapped or traded"
++ 'Trapped' is no problem: Bg7 and e5 together hold a firm grip over central square d4.
'traded' is a problem: it leaves you weak on the dark squares. That is to be avoided. For example if white plays Be3, Qd2, Bh6 to trade Bg7, you can avoid the trade with ...O-O, ...Re8, ...Bh8

In the King's Indian Defence white has various approaches and the Classical or Orthodox approach for white is positional and aims to give black a bad bishop on g7. A bad bishop is one whose activity is very limited by the presence of its own pawns on the same colour squares as the bishop.

In order to get some kind of activity, black usually plays e5, intending to move the f6 knight and play f5, g5 and h5, with an attack on the K side. Apart from the Bayonet Attack, which is preferred by some players, white will normally play Ne1. The reason for that is the B on e2, which stops black from playing the f6 knight more actively to h5, from where it can cause kingside weaknesses to white's pawns or open the diagonal for the g7 bishop by arranging to be taken on f4, when black will recapture with ef, reopening the diagonal for the bishop. White's light squared B always goes to e2 in these lines. Absolutely never to d3, where it's misplaced and gets in the way. As for black's minor pieces, the favourite piece is always the c8 bishop, which sometimes isn't developed for well over 20 moves. Black accepts that the g7 bishop is his worst piece but at least it can be used for defensive purposes.

This positional line is very strong for white but is rather difficult to play. Hence white often prefers different lines.