I was six or seven years old the first time I encountered this expression. If memory serves me well, it appeared at the end of a Looney Tunes cartoon featuring Sylvester the Cat who despondently uttered the phrase after the last of his many dogged ploys to capture and eat Tweety Bird ends in abysmal, near-fatal failure. After suffering through four minutes of high-voltage electrical shocks, falling pianos, and dynamite explosions, Sylvester finally throws in the towel. He acknowledges Tweety's ultimate victory by burying the hatchet - yes, I believe there was a hatchet in the cartoon - and becoming Tweety's devoted helper and follower.
In our modern world the phrase "if you can't beat them, join them" has morphed into somewhat of a doctrine embraced by nearly everyone including those who classify themselves as pragmatists and realists. Synonymous with expediency and opportunism, "if you can't beat them, join them" also shines a light on the modern obsession of ensuring one ends up the winning side, regardless of what this may actually entail. At its core, the "join them" philosophy sells itself as a positive doctrine because it promises to turn a potential win-lose into a win-win, which is great because there's nothing our modern world scorns more than a loser.
I got to thinking about all of this from the perspective of spiritual warfare, and I very quickly arrived at the conclusion that the "if you can't beat them, join them" precept marks the crux of the enemy's war aims. Unbeknownst to most, the enemy cannot really defeat us; it can only persuade us to defeat ourselves. And the most effective way it can ensure we defeat ourselves is to convince us to switch sides.
Though its arsenal is packed with weapons to tempt, demoralize, degrade, corrupt, entice, invert, and mislead, the enemy possesses nothing which it can actually destroy us.
Sure, the enemy has innumerable means through which it can destroy us physically, but nothing it wields from within its vast array of firepower can destroy us spiritually.
The best the enemy can do is persuade us to spiritually destroy ourselves, and the most efficient means of achieving this is to have us abandon the side of Good and consciously join the side opposed to Good.
The enemy very much wants us to believe that we cannot defeat it; that we are hypocritical, worthless sinners who don't deserve to be on the side of Good; and that joining its side represents the pinnacle of prudence and pragmatism. The enemy very much wants us to believe this because it knows it can do little else to prevent us from joining and remaining on the side of Good.
With this in mind, the best way to beat the enemy is to remain committed to the right side of the battlefield.
We beat them by not joining them.
Note added: Spiritual warfare is a confusing concept for many people, Christians included. In the brief excerpt below, Bruce Charlton lucidly and succinctly describes "the two sides" of the spiritual conflict and what it means to choose the side of Good.
*Note. It is absolutely vital to recognise that the sides of Good and evil are Not composed of what are usually termed 'Good people' and 'Bad People'; nor even of better and worse people. The essence of the two sides concerns whether a person gives their allegiance to Good (i.e. to God and creation); or joins the 'evil' side which opposes The Good (God and creation).
It is about there being only two sides, and a person's choice of which side he identifies-with. Matters of individual behaviour are a separate issue; so that some (or perhaps most) of the people on the side of evil will be better behaved, 'nicer' people than some (or perhaps most) of those on the side of Good. However, over time, those on the evil side will certainly become corrupted by their primary choice - as is currently very evident indeed.