It is perhaps too much to assert that Hartford attorney Dan Klau plays a role roughly akin to conscience in my life, but he does try to correct the error of my ways. Thus, his emails recently tweaking me for writing in opposition to the Connecticut Supreme Court's ruling requiring Cassandra C. to undergo chemotherapy to treat her Hodgkin lymphoma.

Isn't the law really all about drawing lines, and making difficult decisions? Isn't it irresponsible of me, and others, to sit on the sidelines sniping at those involved in the difficult task of seeing that justice is done? How far would I go in defense of individual liberty to make decisions?

The Cassandra C. case didn't strike me as particularly hard. Yes, she's a minor on the cusp of legal maturity. She decided she'd rather run the risk of death than endure chemotherapy; her mother supports her in that decision. The Department of Children and Families moved in to assume temporary custody of Cassandra to make sure she was treated against both her will, and that of her mother.

However uncomfortable I may be with the decision to forgo efficacious care, my blood boils when I see the state move in to substitute its judgment for that of a patient.

How far am I willing to go in asserting this passion for individual liberty?

I've discovered at least one limit: The decision of parents to opt out of immunizing their children for measles strikes me not just as foolish, but as dangerous. As a matter of public health, immunizations should be mandatory, and, if necessary, compulsory.

We'd come close to eradicating measles as a result of the development of vaccines. Yet many parents now opt out of vaccinations, some for religious reasons, others because there is a small risk that those vaccinated might suffer an adverse reaction to the vaccine.

The result is that measles is back. More than 100 people in 14 states were diagnosed with measles in January. Many of those cases can be traced to exposure at Disneyland in California.

Physicians report that vaccination of this highly contagious illness is 95 to 97 percent effective in preventing illness. Those who are not vaccinated pose a substantial risk to others when they are exposed to the illness. Measles is highly contagious. The virus that causes it can linger for hours independent of its host.

Last year, almost 80 percent of measles cases were linked to children who carried the virus and transmitted it to others because their parents refused to permit vaccination as a result of religious beliefs. These parents are medical Luddites, and while they are entitled to believe whatsoever they like, they are not entitled to place the broader public at risk.

So my partial answer to Dan Klau is as follows: A parent's liberty to accept or reject medical care, including vaccination, ought to be limited if the exercise of that liberty poses a serious and imminent risk of harm to others. Refusing measles vaccination poses such a risk. Children ought to be vaccinated, if necessary, against the will of their parents.

Where does that leave Cassandra C.?

I still say she and her family were within their rights to reject chemotherapy. While I am troubled by what appears to be their shortsightedness, I respect their autonomy. Their decision might result in death to Cassandra, but it does no harm to others.

In the case of immunization, the harm a parent does by refusing to permit vaccination of a child poses a great threat of harm to others. It is not at all clear to me why I should run the risk of serious illness or death just to accommodate the bizarre and idiosyncratic beliefs of others.