That simply isn't true, it is a mathematical fallacy people often fall into when dealing with infinity.

To take an extreme example, imagine that ALL bitcoins have already been mined, and there are no more bitcoins to be found. Then imagine that they start blacklisting bitcoins at an incredible rate: HALF of all bitcoins in existence are blacklisted each year. Remembering that it is possible to subdivide bitcoins (and arbitrarily far, given minor changes to the protocol), in what year will there be no coins left?

Zeno's paradox is very clearly not the way things work in the real world, or we wouldn't be able to physically move anywhere.

You falsely assume there'd be a fixed rate of coins lost to theft. When there's 100k coins left, though, it's entirely possible that someone goes and steals all of them.

The ability to steal all of them would imply they were all in one place or a small number of places to be stolen, modulo true protocol hacks. That seems unlikely. As they get subdivided, they spread finer and finer on a per-coin basis. It would be no different than trying to steal the entire set of BitCoins today. If you think that can be done, go for it.

Keep in mind that the coins can be distributed in very minute amounts. So with 100k coins remaining in circulation, that could be billions of people that all hold .00005 of a bitcoin.

The real world has Planck's constant. Exponents can be increased indefinitely, and eventually re numbered, like the New Israeli Skekel = 1000 old Israeli Shekel.