males are intrinsically inclined to have many sexual partners, as opposed to females, because they were biologically designed to spread their genetic material
While I do not have a problem with persons(male and female) having many sexual partners, what you made reference to makes the assumption on the biological function of spreading genes. It makes the assumption that THE purpose of sex is reproduction and uses that to explain why males as opposed to females should be intrinsically inclined to have multiple partners. I don't agree with this (un)reasoning. Sex can be and is driven by various things outside of physical reproduction where this would not apply.