You don't get marked forever for it. Karma system is easy to abuse and you can dodge all consequences by donating a few water bottles to the beggar next to Tenpenny.
If I remember correctly, the sound of 3 Dogs berating you for it continue forever as a part of normal playlist in GN Radio. Which is quite often enough~
It's an important consideration of why I dont blow up Megaton, and/or doing the mez quest (in Paradise falls). Very annoying if turn on radio and hear 3 Dogs berate me for it. It's just a fucking few caps and the questionable juvenile sense of doing bad deed, after all.
But no. Some people apparently dont have any trouble disassociating themselves from said sounds, so they think it's small consequences.
Dont believe me? Just make a save before destroying Megaton. Destroy it. Then play 2 hours after that with GN Radio turn on. Let's hear your opinion after that session.
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Aside from everything else, I said this for destroying Megaton and getting tenpenny players apartment:
It's much more stylish than the shack in Megaton. Honestly, I never can stand that fucking shack, even if I still use it, and redecorate it to my liking.
And 4 merchants at floor 1 of Tenpenny beat all other markets, equal to Rivet City Hangar. Luckily this access is available to all players, not exclusive.