1) You are violating the rights of the Mod developers IF they have said they do not want their works to be included in their mod pack. They don't really need a reason, its their own right so the least you could do is respect it. Your rights ends the moment the rights of someone else start.
This can't be stressed enough. It doesn't matter if you disagree or question their reasons or just think they're being silly, the content author has the right to determine how their content is distributed.
There's a lot of disagreement about whether or not the code used in mods qualifies for copyright protection or not. Does a mod like IC2 count as a derivative work or not? We each have our opinion but the fact of the matter is that it is a grey area and probably will remain so unless specific law is written to cover it or a court of law hands down a judgement thereby setting precedence. So we can quote all the laws we want or point out that Mojang's TOS uses the word plugin (a word without legal definition, btw - ever notice how bukkit "mods" are called plugins :D) but its all rather pointless beyond being an interesting topic of debate.
Now, having said all that, there is one thing in most mods that the people who argue that mods have no copyright protection either forget or ignore, and that's original artwork. All original artwork, be it a painting, sound recording or even, yes, a little 16x16 texture for a mod, enjoys copyright protection and, as pointed out earlier in the thread, it is automatic upon creation. So this means that by distributing any mod that contains original artwork without the author's prior consent you are guilty of copyright infringement. So yes, a mod author could sue, it'd be rather silly due to the costs involved but it is their right to do so. However there is a free alternative that a mod author could use if they chose to, and that's filing a DMCA takedown with the infringer's file host, isp, or even their domain name registrar. To my knowledge, no one has done it but it a viable option that only requires a little homework.
I'm enjoying the civil parts of the debate and just wanted to give a little food for thought. 