The sperm cell is alive. The egg prior to fertilization is alive. Life is a cycle. Like all cyclic processes, it can be somewhat arbitrary where they begin and end.
If life begins at conception, then perhaps it ends when the last offspring is conceived.
The joining of sperm and egg is the closest thing we have to an unambiguous event which can be used to distinguish between the period of time during which a given person exists and the time prior to their existence.
Trying to define a time later than the joining of sperm and egg (which was called "conception" when I took biology) is an exercise which probably cannot succeed.
Women are more affected by these issues than men. When women look past the self-serving aspects of this issue ( meaning birth control ) to examine things such as murder of a fetus and obligations for child support, progress will begin to be made.
The various factions are only about nine months apart in their thinking.
Human cloning makes it clear that a single skin cell can be used to create a human being every bit as deserving of protection as the person from whom the skin cell is derived.
If causing the needless death of a skin cell is not murder, then causing the needless death of a fertilized egg is perhaps not murder (religious views aside).
When, then, during the cloning process, does the skin cell become an individual deserving of protection?
In what way is implantation less unambiguous?