I agree, but afaik some wall placement is just bullshit - an enemy captures a wall next to your base in T1 because you decided to expand the other way (Lajesh for example). So they capture the wall, put a few archers up on there and you, being in T1, have almost no way of defending against that (yea, Hurricane etc, sure, but you know what I mean). Overall these walls I think piss people off the most and from this the prejudiced wall hate just spreads easily. In some maps, however, I think (again, based on my limited low level PvP experience) it's normal to wall up some chokepoints to slow down or redirect the enemy attacks (Uro, Simai).
I think people flame because especially early on it's very hard and annoying to deal with walls due to their instand build and usual low cost. Often walls are just taken to tilt you rather than progressing own control, and being slowed down by a 2k wall blocking off your access to half the map is a pain in the ass. To each their own, I stopped building most walls just because it's standard, but don't really care unless someone tries to fuck me over in Lajesh this way.