But even if there are human constructs that cannot be ignored, my example with police still stands because since the police are the power, they can "construct" rights or deconstruct them still, which means they can ignore rights if they are just a human construct, a construct that they themselves supposedly helped build.
In fact, your argument is really in favor of the ideology that the strongest deserve to rule the weak. That is not the case.
That's kind of irrelevant. Ideologies are great, manipulative things, seizing every argument and foothold they can to support themselves. Saying “nobody actually exists” counters “the strongest deserve to rule the weak” quite nicely, but it isn't true; arguing “people really exist” is an argument in favour of that ideology, but that doesn't make it false.
The idea of God-given rights has, historically, been the major justification behind “the strongest deserve to rule the weak”: https://en.wikipedia.org/wiki/Divine_right_of_kings Does that make you less inclined to believe it? (The answer should be no.)
Ignore manipulative, harmful ideologies until you can shun or counter them. If the Evil Ideology monopolises certain truths, and is the only set of philosophy (that purports to be) grounded in those truths, it seems to all but philosophers like the Evil Ideology is a consequence of those truths.
In fact, if humanism is about human agency, then I am saying that police officers who give themselves the right to shoot people are violating humanism because they violate the agency of others.
That said, rejecting God, rather His principles, will lead to authoritarianism because as man turns away from the principles of correct living, he becomes more of an animal and must be governed. Thus, authoritarianism arises.
No, it doesn't. Language is a human construct,¹ and yet there's yaught bleep mÜOL87 øō°0o. So something being a human construct doesn't mean you can safely ignore it.
¹: Esperanto, at least, is a human construct.