While Sulphate-free home-care is great for your hair, and may prolong your colour service, not all sulphates are bad for your hair!
Sulphates, are typically used as a cleansing agent. There are many different sulphates out there and some are worse than others. Drug store products typically have a higher concentration of lower quality sulphates in them.
Whereas, most professional products with sulphates, have a lower concentration of higher quality sulphates in them.