as well as Rulefan's eloquent logic in his response, you might also like to consider the situation of removing a rake (as an example) where hand touches sand, or removing a rake with a club and the club head comes into contact with the sand. None of these are penalties.
with regard to the first part of your question, there's one other interesting scenario that is worth mentioning. If your playing partner had played first to his position, and you had subsequently created the pitchmark, as discussed many times he would be able to repair the pitchmark before playing. In such a situation I don't believe you would then be required to rebuild it before you played, it just becomes a positive facet of 'rub of the green' for you.
