The most important concern in the minds of social media users

The most important concern in the minds of social media users is the protection of their privacy. Accordingly, as per the privacy policy released to customers, most social media companies use the latest 256-bit encryption techniques to transmit and store user data. However, recent tests done by several security companies show that 128-bit encryption is sufficient for all practical purposes. Hence, if data security is the only objective, then by switching to the older and cheaper 128-bit encryption, media companies can increase their overall profits without compromising on the security of user data.

Which of the following, if true, argues against the suggested change in the encryption techniques?
>>> Weaken the argument

(A) Surveys have shown that customers are also concerned about whether paid accounts at social media websites offer better features than do free accounts.
Irrelevant. We are talking only about whether companies should switch from 256 to 128-bit encryption.

(B) Most smartphones and tablets still use 128-bit encryption techniques and do not support the 256-bit versions.
Wrong, because it strengthens the argument instead of weakening it.

(C)Although the companies will realize net cost benefits by switching to the 128-bit encryption technique, the companies will have to bear the initial cost of installing the new technique.
In simple English: it will cost some money to switch to 128, but in the end it will be worth it ("the companies will realize net cost benefits").
The text says:

Therefore option C strengthens the argument instead of weakening it.

(D)Most consumers do not read the privacy policy of the social media network they are active on.
Irrelevant.

(E)Customer surveys indicate that most users would switch their social networks in case of any perceived downgrade of security features.
The correct answer. If users find out that their favorite social media website has downgraded from 256 to 128, they will leave the website en masse, thus damaging its profitability significantly. That's a very strong reason not to switch to 128.