Right Speech & Precepts

Couple of questions: 1. According to the Dhamma, is it allowed to critisize someone in a constructive manner? 2. If someone gossips about me how do I deal with it? Compassion and kindness aside, sometimes it is necessary to be assertive. One can only be compassionate if one is healthy inside in that moment in time. 3. Intention is a little bit more important than the act itself, (isnt it- at least in Buddhism) (only in a few instances is the act more important than the intention for example stealing is wrong even if one's family is poor), however, if for example I slice my bread in the supermarket and I see remaining pieces of bread in the machine and I take them with me because no one did I then so no reason why I would largely violete the "not taking what is not given". Sure, it wasn't given but if my attention or thought is: "Well, if I don't take it it will be wasted" then that should rather influence my kamma, right? So it's largely about my intention. If I hurt someone out of compassion because he attacks someone and injures them severely I have better results because my intention was to safe others, correct?