It's a catchy quote. It's concise and it conveys a point in eight words. But the quote itself cannot be rested on in and of itself. When you have a catchy quote like that, it is very easy to rest on it. But in the end, it's just a quote and nothing profound. Deserve is a totally subjective opinion and there is not always an objective definition of what liberty and security are either. There's two problems with it. First, inconsistent application. A Democrat might use the argument to oppose the Patriot Act but then support business regulations. Or a Republican might use the argument to oppose gun control but would still want lots of other things banned. Not saying it's impossible to use it consistently, but good luck finding someone who does. Second, everything political trades security for liberty. If you are an anarchist, I give you a pass. Otherwise, no. If you support government, you are trading away your freedom. If you support any form of taxation whatsoever you are giving up freedom. So, yes, there's a balance and it's obviously somewhere in the middle. But the solution to the problem isn't to complain that we should never give up our liberties. But rather to establish the boundaries of what's right and what's wrong. In both cases, people use the absolute to reject their opponents with ease, yet they don't abide by it themselves.
"Those who choose security over liberty deserve neither" is not a very good argument