Yes, I agree, there is an is-ought distinction. I'm not a moral naturalist. I discuss the values necessary to create morality here. Morality is those principles that cannot be reasonably rejected in a hypothetical bargain behind a veil of ignorance. You have to value human freedom and reason to be motivated to obey that agreement, but morality exists in that sense whether or not someone has the requisite values to be moral.

>The questions "would you force someone to maximise their personal happiness" and "would you force someone to increase the happiness of humans collectively" are incomparable.

If you are a utilitarian, and welfare is your only standard of ethics, then there is no difference. Both questions only weigh an increase in welfare against coercion. I would argue that coercion in both questions is unjustified, but is there a principled distinction that you have between the two questions where they should be differentiated?