It is not just the dangers, but the schedule - get to bed Day 1 about midnight in Anchorage and be in Seward by 7.30am on Day 2? I don't recommend Seward as a day trip for most people, much less scheduling an 8am tour there. Fine for some people I guess, but I prefer to spend my time in Alaska much differently.
Very late to the comments, but I did this to a greater extreme last year. My arrival into ANC was around 11pm, stayed at the ES in ANC for a very short time, then left early for a 8am meeting in Seward. It was hell, but the drive made up for it, that from a Colorado guy... A month later I had my second trip, which I decided to bring my wife and turn it into a work/weekend trip. My wife and I now talk about Alaska almost everyday, and cannot wait to get back. I really enjoyed Seward, including the day cruise we took to the Kenai Fjords National Park.