Should exchanges be allowed to harvest?
You can't stop anyone from harvesting. Each account makes it's own decision
It's their call no one can stop them. Although I must say I wouldn't do that...
If they really do, I hope they're doing it on some separate node, not on the node they use for getting information.
People hate banks for the profits they make off us but I guess it's ok for exchanges.
Well, this is a problem.
Many people send to Poloniex and increase her PoI. Already at 10%, no way to avoid this, ok?
it is possible attack the network with a significant amount of PoI?
Of course it's possible to attack the network if you have a higher POI score then the rest of the harvesters combined.
I mean I'm not a dev but I don't see why this would be different for POI than for POS, PoW or any other system.