LSD & other psychedelics are not the same as say amphetamine, morphine, barbiturates etc where you pretty much know what you're going to get after taking them. While neurotic side effects (anxiety etc) are best dealt with by either talking to the person or using an anxiolytic (eg diazepam) and letting the experience play itself out, psychotic breaks do need to be stopped in their tracks as generally, the longer they go on, the more long lasting psychological problems they cause.
I've seen plenty of people get horrible anxiety with psychedelics (had some myself, mostly with psilocybin if I'm honest) and I don't think I ever considered going for the antipsychotics like thioridazine or chlorpromazine; the couple of psychotic breaks I've seen though are something totally different - in one case I got the person to swallow some thioridazine (yes I know it's dangerous, but at the time the mental state was a greater danger) and it all worked out well. With the other full psychotic break, there was no such medication to hand and it went horribly wrong for everybody concerned (the other people involved - me included - suffered extreme acute anxiety from watching the person lose it and being unable to do anything to help ).
Knowing what's a neurotic symptom and what is floridly psychotic is difficult at the best of times, but is much more difficult if you're under the influence yourself. Once you've seen a psychotic break, you know the difference (although as I said, if you're tripping yourself the lines can get very blurred), but until then, you're basically just guessing and hoping you're right. Giving someone access to psychedelics is a fucking huge responsibility and can weigh heavy on your shoulders sometimes - which is why I shudder when I hear of irresponsible fuckwits with a load of psychedelics in their possession