My point is simply that the two are not at all equivalent. An open-source license grants additional rights to the person receiving the license, while terms of service restrict the person receiving it. As such, there is no inconsistency whatsoever with saying that one should not be automagically bound by such things just because they clicked through them or they happened to be sitting on a web site that you use. It doesn't matter at all if you violate the terms of an open source license. All that means is that you don't enjoy the additional rights granted to you by that license. You can still enjoy all of the rights granted to you by normal copyright, which means that you can use your copy and make additional copies in ways covered by fair use. If you go beyond that, you're violating copyright, and that is the fundamental problem, not violating the license. Violating the license is only a problem when you want to use some of it (e.g. the permission to distribute derived works) but not other parts of it (e.g. the requirement to distribute source code).

Violating a license isn't illegal, only violating copyright is. I don't think there's an equivalent for terms of service for a freely-available service.