There have been exactly two instances of S&W's with internal locks locking up prematurely. Yes, I agree that it's two too many. But, even the .460 magnum and .500 magnums don't lock themselves up.
The only two reported were a model 329 (.44mag Scandium frame) shooting a full power load, and a scandium J-frame .357 mag, with full power loads.
I had a 442 with the internal lock. I shot standard pressure and +P ammo through it in every weight available, and never had a problem.
If the lock bothers you that much, you can always just take the hammer out and grind off the tab sticking up on the side. That way, the lock can be in any position and it has nothing to engage. It's completely disabled.
S&W was bought from the Brits by the owner of Safe-T-Hammer, a manufacturer of aftermarket locks for handguns. Did you really think that he would not install one of his locks on EVERY handgun S&W makes? It has nothing to do with liberal views. It has to do with business. The owner of S&W was in the handgun internal lock business long before he owned S&W.
Anyway, if I had a choice, I would buy a pre-lock S&W. But, I wanted a 317 snubby, so I bought one. No, it hasn't locked itself. In thousands of rounds, my 442 never locked itself. But, I would think twice about having the lock on a Scandium framed .357 magnum or larger handgun.
If the clerk at the shop told you not to shoot +P's, he's completely uninformed, and just spewing idiotic statements out of his trap. With a .38spl, you would have nothing to worry about.