No, no fans needed.
The reason we use glass terrariums in europe is because its the most effective way to keep a stable habitat of your choise inside.
I have used glass terrariums to all my chameleons at one point or another, never had any problems. There is a vicious rumor going like wild-fire on forums of how these "tanks" get stale air and equals death for all living organisms.
The secret is ventilation. There are many different ways to adjust and modify ventilation to get the habitat you want. I would agree that it might be difficult for anyone without any knowledge of glass terrariums to get the ventilation right at once, BUT that difficulty should not be enough to stop anyone from start trying.
I can turn it around and question mesh/screen cages and their inability to keep any kind of habitat diffrent from the surrounding state.