Comment by CamperBob2

   "Customers will damage their FPGAs with invalid 
   bitstreams, and blame us for selling unreliable 
   products."

   This used to be true when FPGAs had internal tristate 
   resources (so you could drive the same net from 
   competing sources); this is no longer the case for 
   modern devices. 

I agree that this is a bogus argument -- nobody would blame the chip vendor for damage caused by a third-party bitstream -- but I don't see what it has to do with tristate logic. The only thing keeping me from shorting out two (or two thousand) ordinary CMOS drivers with an assign statement is the toolchain, isn't it?