The whole Fermi Paradox can be rephrased as: "If they're so many ETIs out there, why don't we see evidence of them?" But that covers a host of unwarranted assumptions (not in any particular order):

1) ETI is very common
2) ETI civilizations are very long-lived
3) ETIs all have a burning desire to explore the entire galaxy as quickly as possible
4) ETI technology will forever continue to grow as exponentially as ours has during the last nanosecond of astronomical time
5) ETI will not be satisfied with making contact with its neighbors, but will want to contact every civilization in the galaxy
6) There is no natural limit to the potential of techology, given enough time.
7) ETI will feel compelled to progress technologically long past the point where their security and curiosity needs are fully satisfied
8) ETI are just like us (or just like we've been for the last 400 years)
9) ETI will not exhibit the behavior every terrestrial civilization, except our contemporary one, has exhibited (after a quick growth in technological capability, social forces put a break on technological development after a plateau of capability was reached
10) Relativistic sub-lightspeed space flight may be easily achievable, but that doesn't mean it is possible. For example, propulsion systems may be available to do this, but there may be no way to protect spacecraft from erosion from the interstellar medium at those speeds. There may be dozens of reasons why interstellar travel is impossible even if we do have suitable propulsion systems.

I could go on...but SETI is a means of getting answers to these questions, we can't fool ourselves into thinking we've answered them in order to evaluate our progress. Any one of those issues could resolve the Fermi Paradox without having to abandon the ETI hypothesis.
And of course, the greatest and scariest possibility of all: building radio telescopes and spaceships may simply not be a high priority for truly advanced civilizations. The Romans
never built clipper ships, although they certainly had the technology.

As for all this talk of von Neumann machines, why bother? Every living organism on earth is a von Neumann machine. There's no pressing need to invent such a potentially destructive technology when we are already experts at it: they're called "babies".

We've been doing SETI intermittently for about 50 years now, but we've devoted miniscule resources to it, as a percentage of our Terran Domestic Product. We've barely gotten started. If we had been devoting even 1% of all our resouces to it, (not an unreasonable assumption for an advanced, stable, motivated and prosperous civilization), we might have already scored a hit by now.