I have a 2 story place with all the networking equipment in the attic.

I would like to mount a few cameras around the perimeter but I just can't fathom drilling and fishing for cables again (I did it once already piping cat5e throughout all the rooms).

Can I run cat5e wires out a soffitt from the attic into the drain and then discretely run the wires around the house via the rain gutters? I guess I can attach them to the tops of the gutters so they're not sitting in water. I plan to get submersible wires.

Has anyone done this or am I crazy to even think of this as an option?

It's not something I would do but if it is impervious to water & unaffected by UV there's no reason I can see not to do it. Normal cat5e cable is neither UV resistant nor waterproof.

Keep it up out of the bottom of the gutter and you'll probably be surprised how long it will last. I haven't done it with cat5 but I have with premade bnc/power cable on one run and it's been fine for a year now. Take care with the connection points at the camera. The run will probably be fine.

You would be crazy Remember, gutters get clogged and then you may have to do more than just unclog your gutters if you do as you described. Makes me shudder to think of it.

You could use 20mm round pvc conduit under the rainwater gutters or assuming the soffits are white you could fix it along the soffits. I use it outdoors and use PVC weld adhesive to seal against weather (not designed to be used outdoors) using the PVC weld adhesive that is meant for PVC waste pipe works well to seal against weather. I wait until everything is fitted then and only then do I use the weld adhesive. It's far cheaper than using direct burial cable and almost as effective.
The best thing is if you ever do need to replace a cable, fishing cable through this stuff is easy.

You'll get clogging as mentioned. Idiot homeowner before us had a rain sensor wired that way and it would always clog and overflow the gutters. Consider adding some encoders to the attic, sounds like you might have a run up there.

Is the OP talking about fishing down through down spouts too? THAT I wouldn't do.

Do the conduit idea