Maybe you should stop ninja-capping...It is only good when the defender of that node is either alone and you know you'll win, or if they left it open.
It is more viable for your team if you defended your main node, and battled it out in middle or something.
I can't tell you how many times we would have a healer either defending our node alone or trying to ninja cap, when i would personally like the healer to come to mid and pop some heals, having somebody else defend the other node.
Ninja capping is a bad strategy. It doesn't work all the time, in fact, it rarely works.
I think the guy had a perfect reason to complain. Sure, people are immature about stuff like that, he was probably being over the top, sure. But, you guys did try ninja-capping...lol.