If you can afford it / are happy to allocate your disposable income to takeaway coffee and enjoy it, why on earth would that be unreasonable?
I make excellent coffee at home and never buy takeaway - I don't get takeaway deliveries , either. Just don't see it as a good value way to spend my money.
People spend on all sorts that I don't: scented candles, nails, spa days and treatments, magazines, premium toiletries and make up, Amazon Prime, Cheese Strings, keeping a pet and so on.
But I do spend on things that I KNOW leaves others aghast because it isn't their idea of a good way to spend time / money.
So if you are happy, and use a non-disposable cup to save our planet, none of anyone else's business.