I am given to understand that the main objection to intentionally destroying an early embryo - be it stem cell research, emergency contraception, or whatever - is the argument that a fertilised egg has a soul and should be considered a person.
I shan't make any arguments for or against the existence of souls - I wouldn't change anyone's mind, and it's not necessary for my argument.
Suppose souls don't exist. Then embryos do not have souls.
Suppose souls do exist and all people have them. Our question reduces to whether the soul is present at conception.
Consider identical twins. They developed from what was initially a single embryo indistinguishable from another.
1. Identical twins have only one soul between them. Or
2. The soul develops at a later stage. Or
3. Some entity, which I shall denote by the name God, is aware of how many people will result from an embryo and gives it the appropriate number of souls. If so, then (a) a soul is not innate to an embryo and (b) I see no reason to suppose that God would give a soul to an embryo which will not develop into a person/people.
In other words, either identical twins only have half a soul each or early embryos - at least up to the latest stage where they could begin to split into identical twins - do not have a soul.
The former does not seem to me to be a sensible supposition. Identical twins are separate people who may develop very different characteristics.
Therefore I conclude that it is not reasonable to suppose that a fertilised egg or early embryo has a soul.