Of course it’s not question to kill a fetus too developed but at the beginning of the gestation it’s just a mass of cells without consciousness.
I think that it's a bad argument because you cannot put a fine border between a so called "mass of cells without consciousness" and an individual. In embryology, you can see how an embryo develops day after day and how the future spine, brain, digestive system is determined from the moment the egg is fetilized. Thus, you already have a future person at that very moment.
Now, you want to find a border between "future individual" to "individual". The problem is that this limit is highly arbitrary and that you could potentially have no limitation of that. Typically, it is a similar version of the paradox of the heap where 1000 grains of rice form a heap. If your remove 1 grain of rice, 9999 is still a heap. If you remove another grain, 9998 is still a heap. You can go on and on until you have 1 grain of rice left: is it still a heap?
To avoid the paradox, you set an arbitrary number to which x grains of rice are not just x grains of rice, but a heap of rice. Same applies with a future individual "without consciousness".
What could be the life of a mother if the baby is the consequence of a rape, if this birth is a danger for her health, if the baby is severely handicapped
Let's be honest, most abortions in the West occur not because of these cases, but because they think of abortion as a random contraceptive method when they oopsie daisy forgot to use a condom and don't want to take their responsibilities.
As for the painful life or dignified one. You cannot really know. I am not so convinced that children who almost got aborted in these conditions would say "I would rather not have lived", can you claim so?