electromagnetism - Magnetic monopoles and special relativity

I was thinking about magnetism as a product of special relativity and the result of this approach to the magnetic monopoles. So if magnetism is a product of electricity(like electricity from another point of view),then why do we need monopoles to exist?I know that many theories predict the existence magnetic monopoles but i am referring specifically to the concept of classical relativistic magnetism and magnetic monopoles,so do not give me answers that are mainly based on what other theories predict.

EDIT: why do we need electric AND magnetic monopoles to describe electromagnetism if the two are the same thing from another moving frame of reference?And if we do not NEED magnetic monopoles,why is there even a place for them to exist in relativistic electromagnetism?

EDIT: I know that the mathematics of the theory allow for magnetic monopoles, but the essence of the question is the following:
If I work from one frame of reference and change to any other frame of reference, there are no sources of magnetism that can be related to magnetic monopoles?

Answer

The idea that magnetism is a side-effect of electricity is deeply mistaken. The sooner you forget about that idea, the better.

Electricity and magnetism are the two aspects of a single phenomenon, electromagnetism. Read that sentence again: They are not two aspects of electricity, they are two aspects of electromagnetism. Electricity does not cause magnetism and magnetism does not cause electricity, but rather special relativity joins them together, just as it joins space and time into spacetime. (See also my related answer here).

For most electromagnetic phenomena, there is no frame of reference in which it is purely electric, or purely magnetic. It is always a mix of the two, although it's a different mix in different frames of reference. For example, there is no frame of reference in which a refrigerator magnet has no magnetic field. In some frames it will also have an electric field, but a magnetic field is there too.

So in conclusion, magnetism is a fundamental physical phenomenon in its own right, not merely a funny way of talking about certain aspects of electricity. For that reason, it's possible for magnetism to contain phenomena that cannot be directly extrapolated from everyday electricity plus SR.

PS: If there are no magnetic monopoles in a certain reference frame, then there are no magnetic monopoles in ANY reference frame. Conversely, if there ARE magnetic monopoles in one reference frame, then there are magnetic monopoles in every reference frame.