Should, or Could...
Some disapprove of the whole concept, and they should certainly not allow themselves such a luxury. For those "on the fence", understand that it is a luxury intensive of power, water, and space... but depending on your own personal priorities it can be a very practical luxury. Other peoples priorities can be quite informative to your own but their approval, and what they consider "needful", is not ultimately important to you (because you are weighing your own priorities).
In my own research, for our full-time living (retirement) overlanding vehicle, I can offer that no physical or practical barriers exist. It is on my "long list", and designed into some of our concepts; the option of modern compact washer/dryers, located interior or in exterior spaces of a vehicle not much larger than a Sprinter van conversion. It has definitely the possibility of making it to a short-list luxury item. But there should be little surprise that our current camping/overlanding vehicle (a Jeep JKU) is not so equipped ;-)
As an example, some concrete information (a couple of years old), on a very compact unit:
View attachment Appliances - W:D Combo Ariston - ARWDF 129 S NA (63064).pdf