2. Do you have a right to use another person’s body without their permission?
The answer is no. Never. A person's body is their most natural property. Using someone’s body, in part or in whole, without their permission is theft, obstruction to liberty, violation of security of person, and assault. Their body is not yours to use. Even if your life depends on using part of someone else’s body, be it their blood, their bone marrow, their kidney, their heart, their lung, their liver, or their uterus, you don’t have a right to use their body without their permission. Your right to life is limited by the ability of your own body. A right to life is a right not to be murdered. It is not an entitlement to steal from other people.
Some people, who agree that a right to life is not an entitlement to steal from other people, claim that, for women, having sex gives an unborn person permission to use her body. This claim is disingenuous for three main reasons. First, the only person who can give permission for a body to be used is the person who owns that body, and sex can be criminally forced without that permission. Sex is biological and permission is philosophical, like how human is biological and person is philosophical. Conflating biological and philosophical concepts leads to false premises. The truth is that the biological act of sex occurs under many different circumstances, most simply differentiated as nonconsensual or consensual. Nonconsensual sex, a serious crime, is sex that occurs without the permission of both partners. Because nonconsensual sex is sex without permission, nonconsensual sex cannot be permission for any person, born or unborn, to use your body. The other type of sex, consensual sex, is sex that occurs with the permission of both partners. Consensual sex can be divided further into two categories: recreational and reproductive. Consensual recreational sex is sex with contraception for the purpose of pleasure without reproduction, and by definition it is permission for recreational sex and not permission for anything else. Having consensual recreational sex is not permission for an unborn person to use your body. The other type of consensual sex, consensual reproductive sex, is sex without contraception for the purpose of creating a new person, and by definition it is an invitation for an unborn person to use your body. On a base level, however, the biological act of sex is itself not permission for anything.
Second, the claim that, for women, having sex gives an unborn person permission to use her body is disingenuous because permissions can be rescinded. People have a right to liberty and to security of person, thus people have the prerogative to revoke permission for the use of their body at any time and for any reason. To imply or claim anything less is to deny people their right to liberty and bodily security. Having consensual sex and becoming pregnant is not a crime, therefore it is unjust to deny a pregnant person her right to liberty merely because she is pregnant.
Third, the claim that, for women, having sex gives an unborn person permission to use her body is disingenuous because having sex does not ensure a resultant pregnancy, and in the case sex does result in pregnancy, an unborn person cannot exist until more than 5 months after the sexual encounter (based on the First Question's conclusion), which means after a sexual encounter that results in pregnancy, a woman still has months of time during which she can prevent an unborn person from coming into existence within herself.
In sum, the act of having sex itself does not grant permission for anything, and no person has a right to use another person's body without permission.
The short video below by Blue Seat Studios explains how permission (also called consent) can be granted or denied.