That was the point of picking Juve. Aside from perhaps Munich, no other group winner can defeat them IMO.
I agree with you to an extent, as being emotionally invested in a game really turns up the excitement. But I watch tennis or football matches sometimes with no previous agenda, and my loyalties will be decided as the game wears on. The team or player that impresses upon me the most will be the one I cheer for.
I rarely start watching a sport as a neutral and end it as one too.