A. Intuition.
P1: If morality is objective, then we can expect virtually universal use of a standard set of moral principles.
P2: All humans use and appeal to this standard, if only subconsciously.
C1: Morality is objective.
Seldiora messed up here whenever they only objected to MisterChris's second premise though his first premise is cleverly disguised as something that seems apparent, the use of the word, well, use is what unwraps it.
Let's take a closer look at premise 1 to illustrate what I'm talking about.
If morality is objective, then we can expect virtually universal use of a standard set of moral principles.
If morality is objective
Notice that the premise starts with an If, emulating the popular If x, then y, style of deductive reasoning, a conditional statement to simplify for the general public. Essentially, this is true IF and ONLY IF the next phrase can be demonstrated true.
then we can expect virtually universal use of a standard set of moral principles.
A couple of things, first of all, use? Why use? It is a non-sequitur to conclude that because one uses an objective moral standard that there is one. Why is this the case? Its essentially conflating what the use of a thing is and the actual objective claim of the standard. Everyone could be using the same standard and be wrong. We have seen occurrence after the occurrence of this happening throughout history.
For example; Everyone believed the earth to be flat at one point, yet does this mean that the earth is necessarily flat? Essentially this is a fancy version of an appeal to populism, and this premise leads to a syllogism which is not valid. MisterChris is presuming that use of x and x's objective correctness are the same, when in fact they are not and MisterChris does not demonstrate that they are.
This is not to say that MisterChris's second premise is true either, let's investigate it as well:
All humans use and appeal to this standard, if only subconsciously.
All humans use and appeal to this standard..
This demonstrates why we should not use intuitive arguments to present their case, as they are often flawed, or presumptuous in some regard. Saying that every single human use one standard is a massive burden, and a single example would demonstrate this premise wrong, but if we were to continue, looking at the aside..
if only subconsciously
Not only is this presumptuous, but if a human mind is what appeals to this standard, and this standard is objective because humans use it, then definitionally it can not be objective. As objective is something which is true independent of a mind.
Therefore this conclusion
Morality is objective
Is rendered bunk, neither valid nor sound, as well as heavily fallacious.