Why do you agree with article?
For many reasons.
While I am a Lutheran, and hence have a different philosophy of what “vocation” means, in the Catholic sense Msgr is correct. There is no vocation where there is no vows before God.
As a Lutheran, to speak of a “vocation to the single life” is rather odd. I know of many who have said so, until they met a new object of their affection. I know of many who claim said vocation out of pain and suffering for some sort of event. The are using the phrase to either rationalize the pain, or cover it up.
I know of few who are really called to a vocation that precludes a family. A few pastors, a handful of missionaries, and a person who has dedicated their life in service to God. None of them state it as “I have a vocation to the single life!” but as “I am called (vocation) to do X”. Being single may be a part of that calling, but it isn’t the calling.
That doesn’t mean those who, for whatever reason, are not married should be shunned. Many churches put heavy burdens on those who are single with out realizing it. There are many support functions and out reaches for families, there are few for those who are single. Part of the reason is the ever present fear of lawsuits (which is why you don’t see the singles groups you used to at churches any more). Some of it is that they are easier to forget. An old pastor of mine made a special point to set up Bible studies and events for single adults. Not as a “mixer”, but as a way to say “We view you as valued members of the Church and our family”.