Why these warnings in Revelation?

[Vox]

Is it not part of the Bible? How do you know it isn't, or that the rest of the Bible, or parts (?) of it, are genuine revelation. That's the problem, people been deciding what God says, and what It really means, since man's been thinking at all--either by committee, or a single monk in his cell.

Being PART of the Bible does not make it even equal significance to the Scriptures.
and taking few words out of context to make it fit your agenda - may help you to start a new profitable sect, but it still does not change the fact you are manipulating the words to fit YOU.

and you conveniently ignored the second part of my post
I'll repeat - if YOU are a historicist or a futurist, that does not mean everybody else is.

Most theologians are preterists, with some being idealists and that tells it all.

Citation? How do you know most theologians are preterists?

by history of the Church and Church doctrine.
The vast majority are preterists with idealists mostly represented by Eastern Churches.

Historicists and futurists are the invention of the last 200-400 years and belong mostly to protestant denominations.