Given X amount of hashpower and Y difficulty, the time to find a block on average is 10 minutes. The block time is manipulated by adjusting the difficulty, so your statement is incorrect. If you want 1 minute bitcoin blocktimes with the same amount of hashpower that exists today, you must decrease the difficulty by a factor of 10, you can't get around that. So you see, decreasing the time between blocks does nothing, it just decreases the difficulty and thus the security.
So I say again..security of the blockchain given X amount of hashpower is proportional to time, not blocks.
Your belief is a common misconception.
Higher block frequency should make the network more secure because, basically, there's more "samples" so the appropriate winner wins more quickly. It's easier for someone with, say, 30% of the hashpower on the network to get lucky a couple of times than to get lucky 20 times. Higher block frequency means less time with the rebel chain in power because things will regulate more quickly.
Higher frequency should also make a 51% attack more effective, but the network's kind of screwed then, anyway.