I think /u/BLToaster in /r/nfl said it best.
If you believe this was a fine play call then your football knowledge is very poor. This call could not have been any worse.
First off the blatantly obvious choice of play (as several have pointed out) is a run. Whether that is handing the ball off to your tank of a RB or just pushing a QB sneak up the center's ass this would have been much better. They had ~30 secs and a timeout and would have been able to get off 2 maybe 3 plays if run efficiently for one yard.
More often than not even against a goal line defense this will earn you one yard (and a SB championship in this case).
But let's go against logic and try to surprise them with a pass as the Seahawks did. The OC said they were very time conscious and wanted to use the whole remaining time. Why call a one step, 3 second pass play then? It makes no sense. Also this pass was 100% pre-determined, there were no other options on the play. This is a HUGE no-no in football.
Whenever you are putting the ball in the air you want to have multiple options 99.99% of the time - and that .01% is not on a goal line play for the SB championship. So let's go against logic further and opt to run a one option pass... You know the defense is going to be heavy stacked in the middle because they are expecting the run (as the Pats had said they were) so this is where you should NOT be throwing it. A slant is one of the easiest routes to jump and intercept, so you saying this is a low odds chance of happening is completely off especially when a QB gives a tell of the forthcoming play like Butler said Wilson did. Also, Wilson's pass was not ideal at all - it was too high and inside giving Butler a huge window for a pick. With the defender playing aggressively inside that ball needs to be tight on the back side hip of the WR.
So to summarize - Seattle called a non-time wasting, single optioned, easy to jump pass into a clogged middle defense. Yes, that is the WORST possible call you could have made. If they were set on passing & running time off the clock it would have made much more sense to roll out Wilson, give him multiple options at different levels but also give him the opportunity to run it in.
There is 0 logic in this play call and I welcome anyone to try and argue otherwise with me. Malcolm Butler made an absolutely phenomenal choice to play aggressive against that route but in reality on a goal line situation that is the only way to play against a quick slant...so he basically just did what any other CB would do. It wasn't anything spectacular, just the right situation for it to happen.