It's not so much kindness that if Finnick doesn't want to be involved, then he's a liability. And in truth, he likely would've gone ahead without speaking to him about it at all, but might as well show the other Lord a little respect, right? Keep him semi-informed.

"It's old magic," Eames frowns lightly, he's still figuring it out in truth — the spell is quite a bit older than him, but he can probably manage it alone. Still, "a little extra power when it comes to casting wouldn't go amiss."