Ben Shapiro vs Neil deGrasse Tyson: The WAR Over Transgender Issues

[Sheldon]

Whilst I'd agree that it is immoral to cause unnecessary harm, this is a subjective claim, it is not objectively true that causing unnecessary harm is immoral, obviously. That there is a broad consensus on any moral assertion, or even were it a universal consensus, doesn't make that moral assertion objectively true. 

Ultimately all moral assertions rest on subjective claims, though once we agree on a moral assertion, we can of course make objectively true claims about how to best avoid those immoral acts, or achieve moral ones. For example if we agree it is immoral to cause (I would add the word unnecessary here) harm, then it is objectively true that punching someone for no good reason is immoral, but the moral assertion that causing (unnecessary) harm is immoral is still a subjective one.

It depends on how you define morality.
If you define morality as = causing harm is immoral.

That's not how morality is defined:

Morality 
noun
1. principles concerning the distinction between right and wrong or good and bad behaviour.

Ultimately all moral assertions rest on subjective opinion. 

If you define morality as = causing harm is immoral.

Then, if person X punches person Y, person X is causing harm. He did an immoral act.

This is still a subjective assertion, all you have done is use a begging the question fallacy to assume your conclusion in your opening premise, it is both arbitrary and circular. Also moral assertions are relative, what if you punched someone for example, to prevent a greater harm, like murder or rape? 

Note the notion causing harm is immoral is a subjective one, not an objective one.