Because of energy use? Depends on your perspective. Is any use of energy inherently bad for the environment? if so, then obviously the answer to your question is yes!
Now, does it depend on the type or source of energy used to mine? IF so, the mining activity's eco-friendly status depends on that source and will be different by miner.
What is undeniable is that bitcoin or cryptocurrency mining is yet another example where finding the cheapest energy source benefits the operation. That will force most miners to find energy that's free or most efficient - think hydroelectric, solar, wind, geo thermal. That's why places like Iceland have become hotbeds for cryptocurrency mining.