ERV FAQ: Isn't this just circular reasoning, assuming evolution to 'prove' evolution?

No. No assumption of evolution is made when concluding that commonly located ERVs are due to common ancestry.

A conclusion drawn from evidence and reasoning is not an assumption or a presupposition.

The conclusion is drawn from the following items of evidence -

1. ERVs have the same detailed structure as retroviral proviruses. This fact does not require us to assume evolution.
2. Retroviral integration does not target specific loci in DNA. This fact does not require us to assume evolution.
3. Inheritance places the same genetic material in the same locations in DNA. This fact does not require us to assume evolution.

But it does seem to me that evolution-deniers assume evolution is false when trying to prove it is false...

The accusation of "assumption" is especially risible coming from fundamentalists who adopt "presuppositions" based on thin air - nothing but the desire for something to be true. This is manifest in the "statements of faith" that are required by contributors to professional for-profit creationist blogs.