Well, it's hard for me to not to sound like a complete hypocrite on this issue, but I have to agree with Bob, for a number of reasons:
Bats are very congregational and social animals
, they need to socialize with their own kind. Having just one deprives them of what I believe is something fundamental to their wellbeing, attention from a human keeper is just not the same - and they don't really seem to appreciate human interaction much at all anyway. Having multiple bats just increases the amount of space needed, the amount of care and attention needed to keeping their environment adequate, and the amount of food, which brings me to my second point:
Most North American species of bats eat a wide variety of flying insects. Not easily feasible in captivity. Rehab facilities tend to mash meal worms
and mix in vitamins and so forth, but those are generally considered to be temporary solutions until an animal can be released and feed on it's own. Fruit bats on the other hand are not difficult to feed in captivity, but they are exceedingly messy. You have to think, all they eat is fruit pulp... well, it kinda comes out the exact same way it goes in - and they eat a lot. Much more than one would think an animal their size could eat. Not to mention, our store bought fruit is much more rich than a typical fruit bat would be coming across in the wild. I have no real evidence that a higher fiber, higher protein diet would be detrimental in any way, but that's just it - who knows? No one makes Purina Bat Chow. Plus, waxes, pesticides, herbicides, and all the other random things we put no our produce makes one really appreciate the organic markets.
Another thing is that they can't just be caged like a parakeet. They need specialized housing so they do not harm themselves. Their wings are extremely fragile, and if they were housed in almost any kind of cage, could easily be caught between bars and break or tear the fine tissue. They need enough room to fly around, along with enough perching space for each bat in the colony to limit disagreements - which though they are social, happen frequently and noisily.
Lastly, almost every place I'm aware of considers all species of bats a disease hazard (even though this is highly exaggerated). There may be loopholes in the law to allow one to keep them as a pet depending on where you live, but I guarantee you, all it would take is one complaint from anyone, and any pet bat you had would likely be confiscated and put down.
I certainly don't want to discourage anyone's interest in bats. They are amazing, fascinating creatures, but I'm with Bob in recommending you volunteer for some place that does bat rehab and education. Get some first hand experience with them, and then see how you feel.