Carbon forks can be much stronger than steel. On the way to this year's Furnace Creek 508/Trona 353, I had a wind cover on my steel Rodriguez fixie with ENVE 1.0 carbon fork that was on the rooftop Thule fork-down rack. Although the clamp was shut tight (but not locked), the force of the wind on the cover created so much upward force that the clamp popped open. The bike came off, tearing the plastic strip holding the rear wheel, and I could see the bike bouncing down the freeway behind me at 75 mph. Fortunately, it came to rest on the shoulder, so it didn't get run over by the truck coming up behind us.
However, the only damage to the bike was to the left front dropout, where the front was worn away, so I had just more than half a left dropout left. The frame was still perfectly aligned (True Temper OX platinum is VERY difficult to cold set!), the forks were still perfectly straight, I could ride no-hands at low speed, the bike did not shimmy on fast descents (it's a fixed gear bike, so my descents are at about 55 kmh max). Anyway, the fork was still able to securely hold a front wheel (although the end of the QR skewer was a little askew), enough to finish the Trona 353.
And this is the ENVE 1.0 (300 grams), IMHO the best carbon fork made. I've since got an ENVE 2.0 (350 grams but about $100 less) that will go on the fixie next spring. Something to be said for US-made products (I try to buy domestic, rather than Chinese, whenever I can - the quality is usually worth paying extra for).
That said, I want to use a front disc brake over the winter on this same fixie in order to save wear on the front rim's braking surface. I am tired of wearing out rims, especially front rims, where a sudden failure could be dangerous, and rims seem to be made with thinner walls these days... Carbon seems to be the best material for a fork strong enough to handle a disc, but no one makes a carbon fork for discs with a straight 1 1/8" steerer AND an axle-to-crown distance of 370mm (road bikes). They make this for cyclocross bikes with a 400mm axle-crown distance, but this would raise the front end and affect the trail, and therefore the handling. ENVE's disc fork has the 370mm axle-crown dimension, but the steerer is tapered (1 1/8 to 1 1/4"). I don't understand why the bike industry has not cottoned on to retrofitting road bikes with a front disc; seems like a profitable no-brainer to me! What would make more sense than running disc front/caliper rear for those still wary of road discs on long, steep descents?
So at this point, it would seem to make sense to have a steel fork custom built (by a reputable US builder) to the proper dimensions and with the standard disc braze-on. I see this as about the only justification for a steel fork these days.
Luis