bballman - could not agree more! Big difference between cheering on the home team and yelling/screaming at each play/call that goes against either the team of your kid. A little polite feedback to the umpire is not a bad thing. Calling out the umpire generally gets you worse calls going forward. I think every now and then an ump knows a pitch was borderline - whether you get the call the next time may depend upon whether you are polite or simply a jerk.
I would ask that the cheering be appropriate for the age group. In t-ball, you are allowed to cheer contact. In 10u you can cheer the hard hit ground ball that gets bobbled. Once in high school, please don't cheer when the opposing team flubs the ordinary ground ball or perhaps overthrows first after making a nice grab. Let the play die down down and then encourage the baserunner.
I'm enjoying high school ball and much prefer winning to losing - although a tough loss to a good team can be more satisfying than beating a clearly overmatched team. If I had to sit there perfectly silent and actually be ambivalent to the outcome then I probably wouldn't bother showing up. In conclusion - cheer appropriately!