It's not an idiotic waste of energy if:
1) The energy would otherwise come from other, equally high grade (or even higher grade) energy sources, e.g. natural gas
2) The energy would otherwise come from non-renewable sources, e.g. natural gas
3) The energy would otherwise not be used at all due to overproduction
The monetary value of electricity flowing back into the grid on net metering is extremely low - much lower than the cost to purchase that electricity from the grid. If you have a choice between selling the power to the grid or using it to "generate low grade heat" with an electric stove, then the stove wins just on financial grounds.
If your argument is that you could use direct solar thermal methods to generate that heat - skipping the conversion to electricity - then sure it would be more efficient that way. When the source of energy is free, however, and you have already invested in the infrastructure for other reasons, it makes perfect sense to utilize solar electricity for cooking and cleaning. The alternative is to invest even more on additional infrastructure to utilize the same free energy source in a moderately more efficient way.
Use it or lose it, as they say.
=Smidge=