The most charitable interpretation of this claim is that it's based on extreme cherry-picking. The most accurate interpretation is that it's wrong.
And the most important underlying points are that (1) some attrition is inevitable and normal, and (2) the most aggressive interpretation of the statistics places the attrition rate about where experts expected it to be--at somewhere in the 2-3% range per month.
That figure recognizes that the individual health insurance market, which is the segment addressed by the ACA exchanges, is extremely volatile, with a sizable proportion of people moving in and out every month. Here's how the assiduous statistics-tracker Charles Gaba recently described why people might have dropped their exchange plans after signing up:
"Maybe they got a job with benefits and didn't need the [plan] anymore. Maybe they got married to someone who was already covered. Maybe they moved out of the country. Maybe they turned 65 and moved over to Medicare. Maybe they fell on hard times and moved onto Medicaid. Maybe their spouse or child passed away. Maybe they passed away. Who the hell knows?"
For these people, he observes, the law is working exactly as planned, giving them "the peace of mind of decent healthcare coverage for however long they need it before they move onto some other coverage. For some this may only be a month or two; for others it may be years. This is a good thing." (Emphasis in the original.)
The IBD piece says Aetna "had 720,000 people sign up" for ACA exchanges by May 20, according to an Aetna spokesman. IBD continues: "At the end of June, it had fewer than 600,000 paying customers. Aetna expects that to fall to 'just over 500,000' by the end of the year." IBD's math places the attrition rate at 30% (720,000 falling to 500,000).