Today’s early home pregnancy tests allow you to test as soon as 6 to 8 days after ovulation. So yes, it’s quite feasible to know you’re pregnant within 14 days after conception, if you’re alert to the possibility and testing for it. You’re right that physical symptoms such as morning sickness and amenorrhea (cessation of menstruation) aren’t likely to manifest themselves that soon, though.
A couple of other points:
The argument about “experts” agreeing on when life begins is a red herring. Nobody denies that the few minutes or hours of cell interaction after sperm hits egg do produce something that is reasonably described as “a new life”. It’s there, it’s genetically unique (unless it’s twins), and if all goes well it will develop into an independently living baby. That’s good enough for me to call it “a new life” in a biological sense.
The real question is whether that new life is immediately considered to be a fully developed person, with all the individual rights that full persons have in our society. That question is not a matter of biology, but of opinion and law.
It’s obvious that in many ways our society does not consider embryos and fetuses to have equal status with full persons, and not just in abortion law. They are not counted in census surveys, for example, and they don’t qualify for tax deductions. Women who have spontaneous abortions (i.e., miscarriages) do not have to report an accidental death to the authorities or risk investigation for negligent homicide.
A fetus has an intermediate status between being a full person and being part of a woman’s body, and it develops from the latter to the former over the course of gestation. Which is why the law in general doesn’t consider it to have an independent identity and other features of full personhood until it’s born. And it’s also why the court has decided that a woman’s right to control her own body outweighs the fetus’s right to live, at least in the early part of its development. (In the later part, though, those priorities are reversed. All states are allowed to ban abortion entirely, except when the woman’s life or health is at risk, in the last trimester of pregnancy, and all states do so.)
The arguments that illegal abortions (at least in the US) are safe because few of them resulted in actual death is also a red herring. Complications from self-induced or improperly-performed abortions include perforations of the uterus, retained placentas, severe bleeding, cervical wounds, infections, poisoning, shock, and gangrene. Just because most of the women who experienced such effects after illegal abortions didn’t actually die of them, doesn’t mean that there wouldn’t be significantly increased health risks for women trying to obtain abortions if they were made illegal again. Assuming that chemical abortifacients would just eliminate the problem in practical terms is, I think, being too simplistic.