Marriage is fine as an institution but bad as a habit
Well I guess that he wasn't against marriage but he just didn't like the reality of it. In other words, marriage good as a part of this society (no way to know the reasons why he thought that) and bad because everything becomes routine (boring).
Buster Keaton had only been married for three weeks and never wanted to join the 'Why, dear' club.
Anyway what do you think is the meaning of that quote?
It is all up to personal preferences and what you expect from it.
In my opinion institutions are good, we need to follow some sort of rules in society, so marriage is good. Marriages are habits in the long run, as habitual life is human nature.
Well it is his opinion and he is entitled to it