Trees as fixed gear?

I've already posted this on UKC because I thought it provoke an interesting discussion (or at least an interesting argument) among the posters but I thought I'd get it down here as well.

Basically the new slate guide has come out and thumbing through it with Rach we spotted a picture of Mark Dicken and Ioan Doyle doing Giddy Variations on a Theme (E2 5b) on page 303 (if anyone whats to know). Apart for suddenly catching my imagination almost completely this picture started a little discussion between the two of us.

Rach: So what grade [Giddy variations on a theme] is it then?

Me: E2 5b

Rach: Why though? It's just a slab, isn't it.

Me: Yeah, but it's probably sustained 5b climbing for most of the route and [referring to the original picture] there isn't much gear in it and there is some long run outs.

Rach: So, why isn't it just bolted then?

Me: What? Why would you bolt it?

Rach: Well because it's in a quarry, why else?

Me: but but it's a slate route, it's different, what about designer danger [see end] ? whats about it's history? what... what...

And as you can probably guess my argument trailed off seemingly based around noble ideals like not bolting things just because it's a quarry, giving the rock a sporting chance and "what about the routes history". However Rach couldn't see why a route wasn't bolted in the slate quarries and thus I explained about slate ethics and the original boom period in the 80's, the slate head and the concept of designer danger and then the recent, and I hesitate the use the word, renaissance where many bolted routes of a more sport climbing nature have been developed. Soon enough she muttered something like "well slate is just a bunch of unbolted sport routes" anyway.

So of course bolting had been brought up and thus a discussion probably took a turn for the worst (bolting is always a bad discussion to have with me, I get quite enthusiastic/enraged). This then extended to all kinds of fixed gear. The concept of "designer danger" came up and Rach finally ended with:

Is is ethical to plant a tree in a crack, so that in 20 years when the tree has grown it can be slung as a piece of gear?

Literally I was stumped (excuse the pun) and I've been wondering about it ever since...