I generally agree with your argument. But I don't agree with a single sentence. 

you said,  "The original purpose of reducing disposable products is disappearing.".

But the whole point of your argument is that tumblers and eco-bags are not being used for environmental protection purposes, not that tumblers and eco-bags are not reducing the use of disposable products. 

The problem is that eco-bags and tumblers are becoming more popular and used as a fashion item, causing environmental destruction, but they still have the effect of reducing the use of disposable products. People don't have to use plastic bags with eco-bags, and people won't have to drink in disposable water bottles with tumblers.