Lawyers and anyone else who has a commitment to security and privacy need to support strong encryption, despite the risk of its misuse by unsavory people. The idea that we can give ready universal access to some people - i.e. law enforcement - and not others - i.e. hackers and foreign governments - is neither practical nor desirable.
If you want to give the government access on demand to encrypted data, you can do it one of two ways. You can use weak encryption that the government can crack. Unfortunately, that means that most other competent hackers can crack it as well. Encryption algorithms are necessarily public. One of the advantages of this is that you have a large research community working on detecting weaknesses and patching them before they are exploited. However, it also means that people are going to figure out how to break them. Putting a weak lock on your house so that the police can get in is not necessarily the best way to keep out burglars.
The other way to address the problem is through a "back door" or universal key. The problem with a back door or a universal key is that if the wrong people obtain it, they have instant access to everyone's encrypted devices. And once a key hits the Internet, everyone will have it, and you will effectively nullify everyone's encryption in one fell swoop. As one might imagine, this does pose a problem for the security of financial transactions or personal privacy or even lawyer-client confidentiality.
It is foreseeable that terrorists could use encryption to kill people. It is also true that terrorists can use trucks to transport loads of fertilizer and accelerant and blow up federal buildings. Yet we do not hold Ford Motor Company liable for Timothy McVeigh's misuse of their truck, nor Monsanto for the misuse of their fertilizer, nor Exxon for the misuse of their petroleum. Axes are designed for use on trees and need to be sharp; the fact that we need to contend with the occasional LIzzie Borden does not mean that we should keep them dull.
No sensible person would deny the horror of dying in a terrorist attack; there are few more searing moments than watching people jump from the twin towers. In evaluating risk, however, one must evaluate probability as well as severity. The fact is that you are more likely to die because your shelf of ornamental law books collapses and crushes you than you are to be killed in a terrorist attack. We greatly exaggerate the risk of terrorism in light of its spectacular and well publicized consequences; it is a classic example of a fallacy based on emotional appeal and the availability heuristic. It is the same kind of reasoning that makes people erroneously believe that we are safer in a car than an airplane.
All of life is a matter of playing the odds and evaluating costs and benefits. In my view, the benefits of secure information and privacy outweigh the remote risk that I might be killed because the police were not able to crack an iPhone of a potential terrorist whom they had identified before the fact and intercepted based on the communications in the phone. Or to invoke Benjamin Franklin's oft-quoted words, "Those who would give up essential liberty, to purchase a little temporary safety, deserve neither liberty nor safety."