The argument that they "strictly reduces harm" is wrong though.
The harms with theese spams are two that I can see:
1. Your computer is taken over and are forced to participate in the botnet
against your will.
By providing a harmles executalbe this harm is indeed reduced.
2. Your inbox is targeted with mails you don't want to read, and have now
way of opt out from.
By just altering the links in the spam the resarches haven't reduced this
harm at all.
They have incurred some harm though.
We'll have to assume that the persons who _DO_ want to buy the products
1. Wants to recieve the mail
2. Want the mail to contain accurate ordering information
By altering the content of the mails the researchers has harmed the
business relationship between theese people and the people behind the spam.
The consequence being that some busnisess are cheated of their investments
and some customers tricked to participate in a research study against their
will while at the same time lost their oppertunity to buy the products they
otherwize would have been able to buy.