Sure an Italian team winning the cl is good for the Italian football, but Milan winning the CL or Inter is a huge damage for Juve because of the reasons I mentioned, Finance! That's the key word, all these things are being run by money, whoever has it more, has the better squad, it's no secret and not a small detail.
The success of Italian teams in Europe is good for the league's standing in Europe, because of the CL seeds and Uefa. Yeah but we are not in the position to think about that at the moment. We are in top 3 and we won't go down let's say the next ten years or more. I am mainly talking about not supporting Inter Milan and Milan and somehow Roma. Because these are our main rivals in the league, I don't want them to become stronger. But I would cheer for Palermo's success, Lazio's Parma's in Europe, I would want them to win the UEFA cup or CL if Juve fails, since they are not our main rivals, that would add quality to the league, and (secure) more points in the UEFA standing.
The best thing to happen for Juve is when Milan, Inter and Roma disqualifies from the group stages this year.