I think one other thing might be look at the weapons vs terrain . . . we have had several discussion about how they lack the ranged punch of some of the other IS designs since they go in for HPPCs, large MRM racks, TBolts, Plasma Rifles, or other 'new' weapons when they rolled out. But put those shorter ranged weapons into a urban brawl and suddenly its not a liability to not reach out with ERPPC ranges, most of the configs become acceptable.
And IMO that is where it gets into the terror weapons and the reputation that got any Celestial taken as salvage slagged. Even when the Clans arrived, the Inner Sphere forces followed their post-2SW gentleman's agreement of avoiding combat in urban settings. With the Clans themselves, it was a sort of mania . . . but when the Word of Blake decided to punish all man for rejecting Blake's wisdom they sought out atrocities. Nukes, chemical attacks, released bio-agents, orbital bombardment of cities . . . none of it was hands off. Throw in the fluff we get about how the MD as a whole looked down on the frails, especially an attitude that was pervasive among the higher ranking and thus more borg'd out who would typically be assigned the creme of WoB production- the Celestials.
And if you wanted to spearhead a assault against a defending force that had been pushed back into a city . . . who would be best, tactically, to lead the way? The difficult to destroy Celestials piloted by elite MD who do not care about frail casualties if it means victory. Punch through that apartment building to come up behind a assault mech by surprise? Regular Blakist may jump over it to avoid civilian casualties, but a MD would have no problem walking through that building packed with frails to further the Master's goals.
Which leaves the civilian survivors traumatized by the sight of a Celestial's shoulder sawing through the right side of the apartment where mom & dad had been sitting on the couch with baby brother when you went to get a glass of water . . . and now that part of the apartment is just GONE. And so are your neighbors, and if you do not scramble out fast enough, you will still be in the building when it collapses into rubble- think Pacific Rim where the girl is holding her shoe as the kaiju and Coyote Alpha duke it out. Trauma with a capital T, and triggered every time you see a Celestial . . . and to a lesser extent, a mech- part of why Stone was able to shove his changes down society's throat. More of the public is going to feel that way when the battles came into the cities b/c there will be more people affected or witnessing that something that happened 5 miles outside of town that went around most of the population.