I cannot really agree with that. I put hot sauce on just about everything. There are many times, when the food tastes great as is, but I still like to add a few drops of hot sauce just to give it more bite.Of course it does,if a professional is cooking food there is an assumption that they have a good idea of what flavours go together and have created a dish a such.
From that perspective,it's fairly rude to come in and assume their food is shit and needs extra flavour with hot sauce.
Of course the reality,as others have said,is if you are eating shit food then taking hot sauce makes sense. If it is a kebab place and they don't have hot sauce,then they don't deserve anybody's custom.