if they want consequences for going straight murder-hobo, they should make it logical. For one, everyone in the town/area will no longer deal with you at all and you'll be either forced to just never come back or slaughter them all, possibly failing all quests. Adding in god-tier guards is a possibility but would only make sense up to a very limited level. Level 20 guards in DND would be silly
A level 20 guard would have to be a retired adventurer and have some sort of injury...possibly a knee injury involving projectiles. Half movement speed but still has 5 attacks per round.
But seriously there will be Dragons, Archmages and other powerful beings in Baldur's gate. If you started a fight and proceeded to slaughter the entire city I think they would manifest.
In DOS 2 you could wipe out entire cities and they would stay that way and never recover.
What I am really talking about is legitimate boundaries. Enemies you cannot expect to defeat without cheating or getting extremely lucky.
