In general, conventional weaponry is more effective at accomplishing military objectives.
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Batman style "poisoning the water supply" isnt really a viable option due to the complexities of pulling it off successfully.
The total number of terrorists is small, and their ability is limited. But that may not always be the case.
Where that gets dangerous is when the horror under discussion becomes democratised. TATP is simple to synthesise (though incredibly dangerous when done clandestinely), and so we saw a rise of bombings and attempted bombings using it as that knowledge spread, for example.
So you are fairly safe. You can only fall victim to heroic terrorist attacks.
But not as safe as that sounds. It is about being a hero according to the attackers head cannon, not your head cannon.
Terrorist attacks are down stream from culture. Keep an eye on what movies, novels, religions, and preachers call heroic. The terrorist attacks of 2052 will be distorted versions of what is heroic today.
The reason we don't see more of this is pretty straightforward. Although we have active imaginations, the majority of people carrying out these attacks are not Walter White. It takes organizational power to pull off an attack like that.
So, most modern military would be keenly aware that the use of such weapons might have long term consequences for them personally and hands the moral high ground to their opponent almost automatically almost immediately. This has mostly negative consequences short term and it's probably counter productive. If that was not the case, we'd be seeing those weapons used in e.g. the Ukraine right now by the Russians. And they seem to have no reservations about targeting civilians otherwise. But it's hard to spin gassing civilians as heroic or patriotic. Even in Russia. Kind of destroys their de-nazificaton pitch.
Even the Nazis did not go there during WWII. Aside of course from committing genocide as part of the holocaust. They did actually develop chemical weapons but they never deployed them on the battle field: https://www.history.com/news/the-nazis-developed-sarin-gas-b...