Valve will not defend you unfortunately, how can they? What you base your mods on is your choice and Valve will leave it at that, and they will not become involved in legal matters having to do with your mod being based on something that is copyrighted.
Why does everyone think FUNimation is so bad for doing this? What about those who were remaking Chrono Trigger for the Unreal 2004 engine? That team did so much work and they progressed so much and all at the same time they delievered A+ quality, until Square Enix sent them the dreaded C&D letter. It's the law, laws are made by a government, not a company. A company has the right to enforce these laws if need be. "It's nothing personal, just business". Meaning that a company is trying to protect it's interest regardless of how small the infringement might be, it is simply survival of the fittest in which that company will make sure that they stay on top.
Thousands of C&D letters are sent out daily, lawsuits are being filed daily, some of them happen to be much worse than the closure of a mod.
You see, mods like ESF, ZEQII, BFP, etcetera affect a companies interest. Why? Why not? You have a mod that is constantly being worked on, that is free, a mod that has the potential of becoming much better than the console released games. In turn the company will lose money. The only thing is that the company saw these mods as a potential threat if they were to continue being developed. These mods might not be a threat now, but as they grow, the ideas grow, the development team grows, there could be a good chance that a mod made by a bunch of amateurs can compete with the retail games.
All of what I said is what I think, so I could be wrong. If so, please correct me.