Why do so many people insist that instead of the Red Sea parting,

that they say it was a much more shallow "Reed Sea", or a simple marsh?

So many maps in the back of so many different printings of the Bible,

draw a path of the Exodus which is not through the deep water of the Red Sea?

The description in the scriptures does not support their thoughts at all,

but rather describes deep water:

Exodus 14:21 And Moses stretched out his hand over the sea; and the LORD caused the sea to go back by a strong east wind all that night, and made the sea dry land, and the waters were divided.

  27 And Moses stretched forth his hand over the sea, and the sea returned to his strength when the morning appeared; and the Egyptians fled against it; and the LORD overthrew the Egyptians in the midst of the sea.

  28 And the waters returned, and covered the chariots, and the horsemen, and all the host of Pharaoh that came into the sea after them; there remained not so much as one of them.

  29 But the children of Israel walked upon dry land in the midst of the sea; and the waters were a wall unto them on their right hand, and on their left.

Exodus 15:4 Pharaoh’s chariots and his host hath he cast into the sea: his chosen captains also are drowned in the Red sea.

  5 The depths have covered them: they sank into the bottom as a stone.

  8 And with the blast of thy nostrils the waters were gathered together, the floods stood upright as an heap, and the depths were congealed in the heart of the sea.

  10 Thou didst blow with thy wind, the sea covered them: they sank as lead in the mighty waters.

Psalms 106:9 He rebuked the Red sea also, and it was dried up: so he led them through the depths, as through the wilderness.

  11 And the waters covered their enemies: there was not one of them left.

Also, why can they not accept that all of Israel could cross the deep part of the Red Sea in that short period of time?

Do they forget the following?

John 6:17 And entered into a ship, and went over the sea toward Capernaum. And it was now dark, and Jesus was not come to them.

  18 And the sea arose by reason of a great wind that blew.

  19 So when they had rowed about five and twenty or thirty furlongs, they see Jesus walking on the sea, and drawing nigh unto the ship: and they were afraid.

  20 But he saith unto them, It is I; be not afraid.

  21 Then they willingly received him into the ship: and immediately the ship was at the land whither they went.

Jesus brought them all immediately across the sea, so he could easily have brought all Israel across the dried Red Sea,

in a shorter time than the skeptics "allow".