Guessing from the interface it exposes, BPC seems to work by making a ruleset matching sites with a battery of possible changes, including resetting cookies (to reset freebie-counters), fetching from Google cache, disabling javascript (for purely client-side paywalls) and by finding exceptions for the paywall (user-agent, referer, IP).
The last one is probably the one that is closest to being a breach of some law. If the plugin did not ship with rules for a lot of sites, it would probably be considered harmless, but shipping a list of the magic user-agents etc. that circumvents paywalls seems risky, legality-wise.
The last one is probably the one that is closest to being a breach of some law. If the plugin did not ship with rules for a lot of sites, it would probably be considered harmless, but shipping a list of the magic user-agents etc. that circumvents paywalls seems risky, legality-wise.