well, what would happen if membranes suddenly disappeared?

If your house has a gate, you can sleep peacefully at night but if it would be left open, you are more likely to be robbed, murdered, etc. So as a plant or an animal cell, they have to be secured.

Cell membranes are integral parts of many cellular functions, ranging from simple containment of organelles and nucleic acids to more complex stuff, such as maintaining ionic gradients, transfer of nutrients, anchoring of receptors, cell motility, signalling… et cetera, et cetera.

But like MrMistery wrote, try to imagine what would happen if the membranes simply disappeared – that should give you the most obvious reasons for their existence.

no membranes, no cells.
no cells, no life.

Well first of all, are you talking about cell walls, or plasma membranes? Assuming you mean plasma membranes, these have a lipid bi-layer (hydrophilic on the outside and hydrophobic on the inside) which prevents the cell system from being contaminated. Instead, there’s little holes that import and export lysosomes, which carry stuff like proteins and waste products in and out of the cell.

syne, you seem to be a little confused about membrane transport, and about lysosomes.
First of all, the only "holes" that are present in the cell membrane are ion channels, which have a tiny hydrophilic channel in the center that only allows the passage of a particular ion.
Other polar molecules pass through other passage proteins (pumps/permeases). Macromolecules (proteins, polynucleotides, polysaccharides) are an exception – they cannot pass through the cell membrane, simply because they are too big. Generally macromolecules pass through enocytosis/phagocytosis/exocytosis. This does not involve lysosomes (with a single exception that I know of – lysosomes are involved in exocytosis that occurs the phagocytosis of bacteria by white blood cells, but that is a very minor process). It involves vesicles. You need to look up vesicles, multivesicular bodies, early endosomes, late endosomes and lysosomes.

Cheers.