However, you need not use a magnifying glass or microscope to find tiny insects. This is because that halachah deals with the human experience, not with objective reality. The Gemara explains that maggots found inside a piece of meat are kosher. Therefor, halachah treats the maggots identically to the meat. Spontaneous generation has since been disproven.
Maggots come from microscopic eggs.
Rav Dovid taught that the halachic ruling is still correct. The microscopic eggs and maggot larvae are not within the realm of human experience. The only cause for the current presence of maggots that we can see is the meat. In terms of human experience, the meat is the source of the maggots. However, since that reality is not kavuah, it is not within the realm of human experience, halachah is not affected by that, and majority holds sway.