I don't worry about it anymore.
Sure, given my druthers between 2 identical models, one with the internal locking system and one without, I'd pick the non-ILS model ... but then I have other methods to prevent unauthorized persons from using my firearms and have no personal need for the ILS. Other folks might well find the ILS a practical and desirable option, though, which is good for them.
I've handled, used and helped support a number of the modern S&W revolvers which have the ILS. I haven't had one which has demonstrated an ILS-related functioning problem, nor have I met anyone who reported it happening to them.
Having discussed it with some various folks at S&W over the years, and having been through a revolver armorer class and spoken with the instructor and other revolver armorers, I haven't come across any first or second reports of ILS problems in LE revolvers.
I'm obviously not saying a mechanical problem involving the ILS is impossible. The revolvers are still machines, after all. There are any number of other mechanical problems that could tie up a revolver I'd worry about before a problem with a properly installed ILS that hasn't been fiddled with by someone, though.
I could see how the bottom leg of the locking arm's torque lock spring could become unintentionally dislodged if someone removed the side plate and started to tinker with the inner workings without understanding how everything worked and was supposed to be installed. Maybe involving a moment's inattention during assembly or even an unexpected failure of a spring (but that could be said for something like 6 other springs in a S&W revolver, too
I know folks who I respect who simply won't own a S&W revolver with an ILS, or any other defensive revolver with a lock of any design, made by anyone. That's their prerogative and I'm not generally disposed to try and change people's minds about issues which don't affect me.
If someone were to dislike the ILS, though, why not simply buy one of the small number of J-frames presently being offered without it? They've started cataloging some without the ILS. The popularity of the limited runs they made without the ILS in the last few years apparently caught their attention. I've thought the M40 or 42 looked interesting, myself (grip safety).
I'll continue to carry my M&P 340 unaltered, with the ILS intact, myself ... as well as my pair of 642-1's and a couple of other J's without the ILS.