Strasburg's mechanics fall into the "safe" or more accurately into the "normal" zone according to the ASMI studies. They are on the bare edge of safe. Those same mechanics help him throw harder, which in turn puts more stress on his arm. If Strasburg threw 80 mph his mildly inverted W probably wouldn't stress his UCL worth worrying about. Not only that he wouldn't have pitched past HS so his arm would have been perfectly safe. The inverted W results in arm lag which in most pitchers results in more velocity. More velocity for a given pitcher means a higher risk of arm injury. Obviously, if a pitcher can throw hard and be effective without any arm lag then it is less risky. That is not the case for many, many pitchers who can only pitch effectively at the major league level by employing mechanics that include arm lag.
Just like it has always been there is a tradeoff between risk and reward. I'm guessing Strasburg feels he's on the right side of that trade still.
The reality is that Strasburg is a bad example to use for this argument. His mechanics are far "safer" than many other hard throwing big league pitchers who have had long careers and he isn't what most people without an agenda would call an inverted W type pitcher. I'll even give Chris O'Leary some props on this one as he does a very unbiased look at where Strasburg is at come initial foot strike. He believes that it is an unsafe position even so, but that is simply a matter of opinion based on anecdotal evidence.