questions about a sentence

Since, therefore, it is unavoidable to the greatest part of men, if not all, to have several OPINIONS, without certain and indubitable proofs of their truth; and it carries too great an imputation of ignorance, lightness, or folly for men to quit and renounce their former tenets presently upon the offer of an argument which they cannot immediately answer, and show the insufficiency of: it would, methinks, become all men to maintain peace, and the common offices of humanity, and friendship, in the diversity of opinions; since we cannot reasonably expect that any one should readily and obsequiously quit his own opinion, and embrace ours, with a blind resignation to an authority which the understanding of man acknowledges not

What is strange to me:

since and therefore juxtaposed. Is it possible? Never saw it like this.

What does carries too great an imputation of ignorance mean?

What makes JL say it would become all men to maintain peace? I do not see his thread of thinking.

What does offer mean in the sentence?

I had to have a nap two times before I waded through this sentence. Dreadful.

Please answer my questions. Thanks