2. It is not reasonable to expect that pregnancy will result, there is a lot of anecdotal and scientific evidence that says it's kinda random.
That's not quite right. Yes, pregnancy is not a guaranteed outcome, but it is reasonable to expect that pregnancy
could be the outcome. If you're not deliberately trying to achieve a pregnancy, then the responsible thing to do is to take steps to ensure that it doesn't happen.
1. What if you did take steps to prevent it?
This is the more interesting question. The anti-abortion camp tends to take the "you broke it, you bought it" philosophy with pregnancy, i.e. if you have unprotected sex, you knew pregnancy was a possible outcome, so you don't get feign surprise when it happens, and now that you created a new human, you're stuck with it. This argument falls apart when faced with the real possibility of contraceptive failure. If you're having recreational sex and using contraceptives in a good-faith attempt to prevent pregnancy, yet the woman gets pregnant anyway, what's the answer? The anti-abortion camp tends to say, "Well, you knew that contraceptives weren't 100% effective before you had sex, and you decided to take that risk. You lost the bet, and now you're stuck. Too bad!"
This argument doesn't work very well, because it negates the role of parental consent. Since having sex without contraceptives has a very real chance of resulting in pregnancy, this can potentially be considered as giving consent for pregnancy to occur. Having sex with contraceptives, however, can just as reasonably be considered as denying consent for pregnancy to occur. Since the "parents" acted responsibly by trying to prevent pregnancy to the best of their ability, do they still hold responsibility for the fetus? There are two ways to answer this question:
- Yes, they are responsible, because they knew the contraceptive(s) might fail, and they chose to take that risk.
- No, they are not responsible, because they took reasonable measures to prevent pregnancy from occurring.
The problem with the first option is that it gives people the following two choices:
- You can have sex with contraception, but if the contraception fails, you're required to complete the resulting pregnancy.
- If you're not comfortable with taking the risk of having unwanted kids, then you must never have sex.
This is not a practical solution, since a) sex is one of the most fundamental urges that humans experience, so you can't expect people to abstain from it their entire lives, and b) it's arguably unethical to force people to have children they don't want.
This leaves us with the conclusion that you cannot be held responsible for a pregnancy if you took reasonable measures to prevent it. Now the question becomes: can you allow abortions only in this circumstance? In other words, if abortion is ethically permissible only if the woman got pregnant due to contraceptive failure, then is it possible to prove that this is how she got pregnant?
For the sake of argument, one "solution" would be to force the man to take a video of himself putting on a condom to prove that he used contraception, but he could easily take it off during sex, so then you'd have to mandate the recording of the entire sexual process. Even if you did this, it doesn't help if the woman is the one using contraception, since you can't very well stick a camera inside her to prove that she has a Mirena coil in place.
As such, we are forced to conclude that you cannot prove a pregnancy resulted from contraceptive failure, as you can't prove that contraceptives were used in the first place. If we assume that forcing people to have children they didn't want is unethical and that using contraception constitutes denial of consent to have children, then we can only conclude that abortion must be legal, even though this will also allow people who had unprotected sex to obtain abortions. If the ideal regulatory framework can only exist in theory and not in practice, then you are forced to compromise based upon what is actually feasible in the real world.