Why do people keep making the comparison to gold mining? It's inappropriate.
Gold mining is bad for the value of gold, because it increases the amount of gold in the world. Eventually, the gold coffers on Earth will deplete and there will be no more gold mining.
Bitcoin mining is necessary for the value of bitcoin, otherwise there can be no certainty of the blockchain. After most of the bitcoins get minted, the mining will still have to continue out of transaction fees.
The cost of mining bitcoin needs to be compared to the cost of gold storage and handling of gold transactions, not gold mining.