A few thoughts:

• Depends how much money you are spending to buy those clothes. If it’s almost the same as the price as new, it makes it easier for the people who buy the clothes new to keep buying more and more stuff.
• If you aren’t spending a lot of money, this is like the opposite of fast fashion. You are making the life cycle of those clothes longer by buying them.

PS. I don’t think we should individualize things like this. A significant chunk of the clothes we buy – and other things as well – are made under miserable conditions and/or by children, and it’s very difficult to avoid all of that. It’s a systemic issue that needs to be solved on a systemic level.