I think you may have misunderstood, although obviously I don't know about the specific example you were talking about.
'Organism' is a word which is used by scientists to refer to certain (normally living) individual entities (where 'entity' could mean any individual Thing - be it rock, tree, single sperm cell or planet). That is the main purpose of the word - it is not used to distinguish between 'organisms' and 'non-organisms' because there is no point. Why would a scientist care if something was an 'organism' or not, unless it was for an etchical debate such as this? My long-running challenge has been for someone to provide a definition of 'organism' to test - so far every single one I've ever see has either included things that aren't organisms (sperm cells, skin cells, transplanted organs), not included things which are organisms (chimera individuals, sterile organisms), not included a pre-viable foetus (any definition which includes 'maintain homeostasis', for example) or be so convoluted as to be unciteable.
As such, 'organism' tends to refer to the point at which the scientist wishes to consider the entity as a seperate living individual. This varies from field to field, as choice et al have posted many times - within human reproduction it can be fertilisation, implantation, viability, and so on. Within other biological fields (cellular biology, evolutionary biology, gaiaology, biological emergence) you can have still more definitions - an 'organism' can be a single human cell, or a planet, or a 'compound organism' like a single jellyfish or ant colony.
When I say 'embryologists are biased', I don't mean "you should ignore what they say". I mean "every scientist defines organism in their own way - and you are just picking one version of that and calling it The Definitive Definition, when it's actually just as biased/subjective as the rest of them".
Point 1) is debatable, because 'lifespan' of an individual tends to be described as starting at birth, not at fertilisation. I have also provided textbooks which say similar.
2) is obvious but irrelevant
3) is debatable because it includes the undefined term 'creature'. It is certainly true (possibly contrary to your position depending on definitions) that living non-organisms become living organisms, because you make this claim yourself, when you say that sperm and egg (living non-organisms) unite to become an organism.
4) contradicts your position, because one of the criteria of life is growth (biological meaning: get bigger) which a zygote does not do pre-implantation. Furthermore, another of the criteria of life is (normally) to exhibit independent homeostasis, which the implanted zygote/embryo/foetus does not do. Either way, this is clearly debatable because you have not defined the 'criteria of life'.