Because that's how arguments work. I am making the claim that x is wrong, based on the premises of a, b, c, etc...because those are the premises that I personally believe to be true and sound, which is the argumentative justification for my conclusion. That's fundamentally what a moral argument is. If morality was objective, then there would be some means of empirical proof that a specific set of premises were somehow objectively correct, and that all others are somehow objectively wrong, but there is not anything like that, nor would it even be possible to do so. Morals are simply the conclusions to whatever set of premises that you accept or believe in, so the only way to justify your morals to others is through argument. For example, my claim that "denying people their bodily autonomy is wrong" is because I believe in the premise of "all people deserve the right to bodily autonomy", and, argumentatively, anyone who also agrees with that premise should agree with that conclusion. No one is "objectively correct" because it's entirely up to the soundness of your argument based on the premises you accept. This is literally the fundamental basis of what arguments are and why we do it...I'm not sure why you are acting like this concept is so complex or new.

You never said that you personally believe those to be wrong, rather you claimed that they are self-evidently wrong...

No one claims that their morals are "self-evident" because that would just show a fundamental misunderstanding of what morality is. Additionally, no one needs to clarify that their moral claims are "just what I personally believe" because that's what ALL morals are...that would be completely redundant to point out, especially in an argument where the entire purpose is to make a case for why others should accept your reasoning over another. If you disagree with any of my moral claims, then you would attempt to question, and/or counter-argue, the premises by which my conclusion is based on, and it's entirely possible (and likely) that the end result is simply that we hold different values, and thus accept different premises. That's why morality is ultimately subjective. It sounds like you either have a fundamental misunderstanding of what morality is, OR you have a complete misconception of what arguments are, because these are pretty basic concepts of human interaction.

...government, or society, or the majority, or whatever you as an anarcho-marxist call it, has the authority to impose this morality on others...

This is not necessarily an argument of morality, but of law and/or philosophy. Because morality is subjective, and every person will have their own morals and basis for their morality, this means that groups of people (such as: a country) will need some way to decide which morals will be acceptable within this group of varying morals. Different people will accept and reject different morals, so how does a society determine which ones they will and will not tolerate? And, obviously, different people will have different answers on how the best way to determine this is (this is literally the most fundamental basis of what "governments" are). This is just the concept of "laws" and "power" and "hierarchy" and all that goes into "who should have the power to make decisions on what people should or should not be allowed to do in society", and that's why people argue...

Why have you claimed that it is "wrong" for me to spread my "Far-right ideology" if there is no such thing as right and wrong?

Because I believe that your values and/or ideas are bad...that's literally what my argument is about in the first place. It's no different than why anyone else would argue that MY values and/or ideals are bad: they disagree with my premises and thus argue against them. What exactly do you think people argue about these things for..?

Secondly, "morality is subjective" does not mean "there is no such thing as right or wrong", it simply means that there is no such thing as OBJECTIVE right or wrong (at least in regards to morality). I believe that MY morals are "right", because my personal values justify them as such, whereas YOU believe that YOUR morals are "right", because your personal values justify them as such (even if your values are just religious convictions). Neither of us are OBJECTIVELY right or wrong, which is why we rely on argumentation to defend the soundness of our premises, in order to convince each other, or others, to agree with our values/reasoning.

And if we can't trust the reliability of the human senses, how can we rely on external tools INVENTED by humans USING THEIR SENSES, to determine truth?

Because tools provide a basis of objectivity for everyone. For example, a thermometer is a tool we made to objectively measure temperature; every thermometer will give the same, repeatable results for any given situation we use it in, because it utilizes an objective metric of measure that individual people cannot provide on their own. One person can tell you it feels hot outside, and another person can tell you it feels cold outside, but a thermometer will always produce an objective value for any given temperature, which will be the same value for anyone who reads it. Tools like this provide a single objective metric that any person can use, thus providing a basis for universal data (which is necessary for any scientific evidence), instead of relying solely on the subjective experiences and perceptions and beliefs of individuals.