Lysosomes are membrane-bound organelles and the area within their membrane is known as the lumen, which generally contains hydrolytic enzymes and other cellular debris.
The key function of the lysosomes is the digestion & removal of waste.
Cellular debris or foreign particles are pulled into the cell via the process of endocytosis.
Lysosomes are referred as bad because lysosomes contain enzymes that break down excess sugars and fats into substances that are then used up by cells.
In its absence, there is an accumulation of fats and sugars in the cells rather instead of being excreted or used.
Since enzymes are unable to break these substances, it causes accumulation in cells and turns toxic, harming cells and organs.