A.i. Can anyone seriously oppose effective altruism in principle? I find it difficult to imagine someone supporting ineffective altruism. Surely, we should let our charity be guided by evidence, randomized experiments, hard thinking about tradeoffs, etc etc.

I emphatically don't, but yes, one can. The quantitative/reductionist attitude you've outlined here biases us towards easily measurable causes.

Some examples of difficult to measure causes include: 1) All forms of funding-hungry research, scientific or otherwise 2) most x-risks, including this forum's favorite AI risk 3) causes which claim to influence social, economic, military, and political matters in complex but possiblyhigh impact ways 4) (Typically local and community-driven) causes which do good via subtle virtuous cycles, human connections, and various other intangibles