It's hard to imagine a soldier carrying out these acts. They all start off as ordinary people so what is the journey from that to a mental state where they will commit those acts on other citizens.
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I heard about one other aspect to Tiananmen - 20 years before Tiananmen the young generation back then perpetrated the Cultural Revolution with all the related mass crimes and violence, in particular against the representatives of the older generations. To them, now 40-50 years old, the students at Tiananmen looked like the start of possibly something similar to Cultural Revolution and having been perpetrators themselves, they were very afraid of such a new thing starting, especially with them now possibly being the target, and this is why the society was in general ok with the thing crushed mercilessly right at the beginning. Again, i'm not a China expert, just heard/read things along these lines, and being from USSR (where in particular young revolutionaries fervor had been a thing) find such situation and its explanation pretty plausible.