Even with its health insurance marketplace floundering for the fourth week, the Obama administration is resisting what some Democratic allies contend is the most logical response to the problem: giving consumers more time to sign up.

According to insurers and the White house, delaying the deadline could undermine efforts to lure a broad, young and healthy mix of consumers to the market. That would end up costing insurers, and possibly taxpayers, money.

The case against delay was outlined in a memo circulated to lawmakers by the insurance lobby last week. The document from America’s Health Insurance Plans warned that delay could have a “destabilizing effect on insurance markets, resulting in higher premiums and coverage disruptions for individuals and families.”

For now, the administration is sticking with the insurers. Health and Human Services Secretary Kathleen Sebelius on Wednesday called delaying the tax penalties for those who miss the deadline premature.