Metal Gear Solid 4 -- Snake/Raiden scene in the Nomad prior to Shadow Moses

1.) In this scene from MGS4 (the Mission Briefing just before the Shadow Moses act) around the 3:05 mark Raiden says:

I won't live a proxy life, a slave to someone else's will.

Snake then replies:

I'm a shadow, one that no light will shine on. As long as you follow me, you'll never see the day.

Is it just me or is there a huge disconnect between these two lines? Is this just bad writing? Or if not why did Snake reply the way he did? What could he possibly mean?

2.) Furthermore at the 3:50 mark Raiden says something interesting:

But once this is over, we will have our freedom. I'll release you, it's the only way I'll ever be free.

Snake then replies:

Raiden, five years ago, that's not what I meant...

What did Snake say five years ago in the Big Shell incident? If I remember correctly he said something about finding something to believe in, but this couldn't be what he was referring to? What was Snake referring to when he said the above? And why would "releasing" Snake free Raiden?

Edit: why did someone remove the MGS series tag? This question is primarily about MGS4 but it also references the older MGS games, and in particular, asks about events in MGS2. Please read the entire question before editing needlessly next time, thanks.