Ok...here´s the scenario:

my opponent has scapegoats on the field, he activates MONSTER GATE and starts dropping his deck (magical explosion deck) and Destiny Hero DOGMAs start to pop out, and he passes them by until an "electible monster" comes out.

Why the hell can he drop the DOGMAs to the g-yard, if monster gate effect stops when a monster pops out of the deck?

he does the same with D-hero PLASMA!! and he does the same with other "this card cannot be special summoned EXCEPT BY" - and he argues that´s the line he needs to drop them straight to the g-yard until one other monster comes.

Now, he DOES THE SAME WITH REASONING!
Why is all this! ???? I looked for the rules...but none applied here!

please help

just look at the text of monster gate:

can dogma or plasma be normal summoned? no. therefore, you don't stop picking up cards.

lets look at reasoning:

same wording. can dogma or plasma be normal summoned? no. so you continue to pick up cards. there's not a ruling on it because it's in the text of the card itself.