Bitcoin is actually becoming an alternative source of income for the unemployed remotely to make a living. It is providing part time work at home globally to all and sundry and so I agree that it's a source of income.
It's a good source of income if you know how to do it well. If you will make this as your main source of living, just make sure that you can do it. For miners, I know they are making this as their main source of income as for sure most of them already got the ROI. And for traders, I think many are already treating it as their career.
Big miners can afford to depend only on bitcoins for living as they have invested huge money into it and they are also making regular income from it but mining is not possible for everyone at this stage and if you have limited ways to earn bitcoins then its better to treat it as an extra income.