Why? Maybe the mako has inertial dampeners like the Kodiak, at most they feel gravity pull in another direction but they wouldn't get whiplash. Besides, look at his driving record. Didn't drive into lava ponds on therum or off cliffs in a snow storm on norevia. If anything, his driving is the reason they'll still alive.
Don't see how security features account for lava ponds or steep cliffs. What about being shot by the geth on Feros or Ilos? Shepard is also pretty good at driving the Hammerhead and those skycars when he forced down an armed skycar driven by a specter in a taxi, in oncoming traffic on Illium
Running the geth over worked for a while... until one of the little bastards thought it would be funny to get stuck underneath it. Thus making it VERY difficult to drive... I cannot even remember how many times that happened and I ended up driving into a lava pit on Therum... ¬_¬