The polygraph is pseudoscience. Of course it can be beaten, it doesn't work to begin with. Why the US still puts so much weight on them when they know they don't work is a mystery to me. Just get rid of the damn things and do your homework better.
It's a psychological tactic, and is all about pressure. It serves as a potential deterrent and mind game that works on multiple levels. Consider it like a scarecrow in a field. Yeah, some of the smart crows will figure out it's just some clothes on a pole, but it still deters and confuses the rest. The only silly thing would be calling a scarecrow a security guard or a polygraph a lie detector test. It doesn't mean it's silly to put a scarecrow in your field.
Obviously it's 99.9% pseudoscience, and obviously it's beatable and unreliable, but I don't think that's the point. I'm sure they're very much aware of that, and still use it because they see the value of it as a psychological tactic. It's one of many lines of defense: if you pass that line of defense, it definitely doesn't at all imply you're not a spy, but if you don't pass it (in any way), the security requirements dictate that the safest option is for them to not hire you.
Absolutely no positive value should be attributed to a passing result. The idea is exclusively to attribute negative value to a failing result. And then, not value in terms of some actual empirical finding ("was this person really being deceitful?"), but just value in terms of whether or not to hire them to handle the most sensitive of secrets.
The only abomination is using it as a consequential determination of truth or lie, or innocence or guilt, like in a police investigation or trial. It should never be permitted in such a circumstance for any reason.