I think, as for so many things, you can please yourself. But for practical purposes :
The French normally only eat 1, as a treat and not every day - especially if they're weight conscious.
A proper flaky croissant from a good bakery will contain 45% weight of butter, so the French don't add butter.
(As with bread, they don't put butter on the table, but it's almost a criminal offence to serve a meal without bread!)
Croissants just need to be very slightly warm to release the buttery smell.
Eating a croissant without making loads of mess with greasy flakes, it's usual to tear off a portion that you can put straight into your mouth, having first put jam on it if that's a choice.
Of course people will still dunk - the same with bread - but you don't see that so often now. The little bowls for coffee or chocolat - which make dunking easier - are more often used at home for a family breakfast.