It's not so much the lack of killing children, as the removal of killing children as a feature. In the original Fallout games, child-killing was a major part of the fun; taking that feature out was seen as an affront both to tradition and to the integrity of Fallout's artistic vision. It would be akin to having a Mortal Kombat game without fatalities, or a Sonic game with the player-character being able to run at high speeds.

Now I'm not one of those bitter, angry, trapped-in-the-90s, hates-everything-Bethesda NMA nerds! But in when it came to child murder, the NMA creepoids had a point.

As for MacReady, he evidently survived his wounds. The massacre is still canon - Mac refuses to discuss Little Lamplight, implying that something extremely traumatic happened there.

It's not even about the removal of an ability or feature, it's actually a pretty common problem with Bethesda in general. No one on their writing teams seems to know how to write a character, so they decided "Hey, kids are always annoying, right?"

The end result is that the most killable characters in the game are unkillable. I'm not saying they should make kids killable, just maybe not make them the absolute most annoying part of the game if that's the route they choose to go.

the way I heard it some or all of the children couldn't be removed, so they made them invisible, resulting in players sometimes seeing "ghost dialog" and even accidentally shooting at one of those children without realizing it, causing entire towns to turn on a player all at once, seemingly for no reason.

Yes, but you can't SEE an invisible child pop like a jelly-filled balloon, so it's okay!

The consequences you mentioned were the other big part of it, though. Killing kids branded you with a perk that caused any remotely good NPC to refuse to speak to you, if not shoot you on sight, for the rest of the game. It was actually worse than becoming a slaver.

Incidentally, looting graves in the old Fallouts gave a noticeable hit to your karma every time, but not so in Fallout 3 and onward. Does Bethsoft condone grave robbing?

In Fallout 2, they forgot to take the kids out of the Den, who were also master pickpockets. So you would have invisible children stealing your stuff every time you went into a doorway.

An entire questline requiring you to submit yourself to being constantly insulted by immortal invincible sociopaths disguised as children for a fair length of time was not terribly enjoyable, no.

And I never even installed the Killable Children mod. But I can imagine that many players did so due to the above horrible nature of said 'children' as characters, rather than simply 'because woo hoo killing kids!'. The comments on the various mods on the mod sites certainly seemed to support said hypothesis, anyway.