When you're basing it off of experience? Not evil. "Every time we've done X, we've suffered a brutal performance hit. Let's plan on either optimizing or avoiding X entirely this time."
When it's relatively painless? Not evil. "Implementing this as either Foo or Bar will take just as much work, but in theory, Bar should be a lot more efficient. Let's Bar it."
When you're avoiding crappy algorithms that will scale terribly? Not evil. "Our tech lead says our proposed path selection algorithm runs in factorial time; I'm not sure what that means, but she suggests we commit seppuku for even considering it. Let's consider something else."
The evil comes from spending a whole lot of time an energy solving problems that you don't know actually exist. When the problems definitely exist, or when the phantom psudo-problems may be solved cheaply, the evil goes away.