Wind against tide - physical reasons why this is dangerous ?

[LeoLind]

Refraction is the change in direction of a wave due to crossing a boundary between two media at an angle. Does not seem too relevant here?
But it can have interesting effects, for instance where waves cross a channel or bar obliquely.

Yes, but regarding waves, refraction refers to the bending of the wave travel direction towards shallower water, such as approaching a beach at an angle, or passing around a shallow headland. I think it usually reduces the wave size as there is divergence, i.e. spreading of the wave energy.