[NYer]

I hope this doesn’t sound ignorant, but is there anything wrong with a wooden altar?

Yes! Wood is temporary. The Vatican is asking all Catholic Churches to replace their wooden altars with a more permanent material such as marble. Why? Because the altar represents Christ.

[wombtotomb]

There is a second, more urgent reason. Wood is porous. If the blood is spilled on it, recovery becomes an issue. I know in highly polished or sealed wood that becomes less of an issue, and I also know that marble and the like are also somewhat porous, but, imagine an unsealed piece of wood soaking up the precious blood like a sponge. No way to recover it and it could be open to descecration....