as a developer myself i have no problem with leaking, if someone is downloading a leak it is highly unlikely they would pay for the content. the idea of making addons paid is to, quite obviously, get money for the time and effort put into the addon. but if the addon gets more real-world testing, more criticism and more overall usage with no to very little change in income anyway, leaking shouldn't be considered an issue. just my thoughts
I don't always approve of it. Depends on the dev. Addons like VCMod shouldn't be leaked, he's very courteous to people and politely asks for them to be taken down. Shitty, overpriced addons with 14 layers of DRM and no support, leak away.