They're concerned that the medication will too easily get into the hands of people who shouldn't be taking it - men with heart disease, diabetes, or other conditions that contraindicate prescribing Viagra. Because in Bangladesh, apparently, you don't need to go to a prescribing physician to get medications; you can get pretty much anything over the counter.
If that were the case, I would think they would be more concerned with other drugs with high potential for abuse, like maybe opiates? But I guess they figure there is going to be a huge demand for Viagra once it becomes available, and everyone is going to run out and get it without really thinking about the consequences.
The government granted the licenses to manufacture the drug in response to reports that the number of erectile dysfunction sufferers had increased, so I guess it's not unreasonable to expect that there might be a rush on the drug once it becomes available. Obviously the standards of care are somewhat different than those in other countries, but maybe they could manage with a public education campaign about the potential dangers of using Viagra.