Gravity "Only a Theory"

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I came across this and it's really got me thinking: http://www.bringyou.to/apologetics/p67.htm The thesis is that there is no "Law" of gravity. Because all we have is an unproven theory. Example: there are two tides every 24 hours, because the oceans rise when the moon is above them and when the moon 12 hours later is on the opposite side of the world. Now, sure, if gravity is attraction, you'd expect the water level to rise in a tide when the moon is above. But if the moon is attracting by gravity, why does the water level rise on the opposite side of the world? It should depress, get lower than normal, attracted downward to the moon that's out of sight. Does science have an explanation? Or is this one of many phenomena in the world that I believe science can't explain and doesn't because it's so right in your face it isn't even 'seen'. Where's Leo when you need him? Would this have him stumped? Also, since water-levels rise away from the moon on the opposite side of the world, is that not replusion ie. anti-gravity, and proof that just as there's gravity, equally there's anti-gravity? Isn't that important??? Any ideas?