In reply to andyathome:
There's a lot of good arguments and opinions herein but I'm detecting a bias towards 'trad is the only true way' and similar views in many of the posts as well as several disrespectful comments towards sport climbers and beginners here.
Frankly, I don't understand this in what has been (in my experience) an inclusive, helpful and encouraging community (both here on UKC and out at crags or at indoor walls). So far I haven't met a climber I didn't like, whatever their preference in style or experience level.
To answer the OP from a relative beginners point of view I saw the placement of bolts as a twofold thing:
1) To adequately protect good/interesting routes where trad placements were potentially unsafe
2) To provide a sport climbing experience on crags/quarries where it was seen as acceptable by the climbing community.
Of course, my own lack of experience may show in those answers but that is genuinely my perception at this point. It may change as I become better informed and more experienced.
I DON'T think that bolts are placed to demark a particular route as 'Just for Sport. No Trad allowed' and it's my experience so far that trad climbers and sport climbers (and boulderers) are happy to mix on a crag.
I would sympathise somewhat with sport climbers that might take offense at the suggestion that bolted routes are done purely for convenience, to provide the lazy option or because doing it trad is too scary. I think those are the types of suggestion that somewhat miss the point of why someone might choose to sport rather than trad - to my mind the two styles offer a different experience of moving on the rock face. Yes, some of that is undoubtedly down to the route itself but still, the same line climbed trad and sport would seem to me to offer a different psychological experience and encourage a different approach each way.
Personally I've only have a handful of outdoor solos and trad leads. I lead sport indoors only at the moment. I want to experience outdoor sport routes as well as doing more trad and I may find I favour one over another eventually. I tell you this so you know where I'm coming from - Please take my opinions in the context of my limited experience.
As for my little group of outdoor newbies, their wants and aspirations vary between sport and trad and their expectation of the experience varies. To put it simply I have a couple of climbers that can't wait to get their hands on my rack (oo-er, missus!) and start placing their own gear but by the same token I have one climber who doesn't like the idea of trad because he doesn't want to have to split his attention between gear placements and the climb itself. Another of my newbies doesn't like the thought of trad because of all the gear involved and wants to strip it down to basics - he pulled his first V.Diff solo recently and actually finds he prefers bouldering.
All that from a group of wall-bred top ropers. Who'd have thunk it?
Note that in no case are any of my group frightened off from trad or are seeking bolted protection because trad looks (or feels) too scary (or even that we panic). Just because we are inexperienced does not mean we'd all want bolted routes - we'd want bolted routes when we fancy a sport-style climb experience.
Is trad scary for us? Yes indeed, but so are E grades, sport climbs, multipitch, mid level bouldering puzzles and so on. Will it stop us from trying it all? Not on your nanny
Now I'm sure I've missed part of the point and I have picked on a few particular viewpoints to counter here but I wanted to offer an honest view from the less experienced end of the spectrum seeing how most of you here seem to have already chose your preferred style and view to match.
In my honest view I don't see why sport and trad aren't in closer harmony and have no real issue with bolting routes of any grade where appropriate. The bit I admittedly don't quite understand is what really dictates where bolted routes will appear or what dictates the acceptable 'ethic' of a particular crag (to bolt or not to bolt?). Is it really just the preference of a handful of regular users of a particular crag or something more widely accepted?
Anyway, sorry for chucking in my two penneth this late on.
Note: Do you know what these 'sport vs trad' style discussions remind me of? The PC master race vs the console kiddies argument from the video gaming community. Both are valid ways to 'play', surely? Aren't we all practising the same sport at it's core or am I just being really naĂ¯ve?