I have no problem with Bell slowing down my P2P transfers when there's congestion. However, from experience, Bell throttles based on time and not bandwidth/congestion.
As soon as the throttling times are over, the P2P downloads speed up considerably, so it's obviously not throttled based on congestion on the network.
As for downloading when it's not affecting others. It would only affect you if they were experiencing congestion, not based on time of day; which is what they have implemented.
Bell is artificially slowing down their customers during certain hours of the day because they are unable to implement a correct solution to handle congestion.