I must be in the minority because I do adjust my tactics depending on the opponent.
Not extensively but I have 3 saved tactics I pick from and tweak accordingly.
When I'm playing against a 3-at-the-back team with WB's, or sides with a narrow midfield, I'll take advantage of the space out wide. For example, I'll start with wingbacks AND wingers, play wide and attack down flanks. The motivation for this is to create 2v1 situations down the flanks and crowd the opposition WB. I usually use 4-1-2-2-1 for this, ideally with a target forward.
If my opponent has 2 strikers, I'll usually play 3 at the back to outnumber them.
If I'm going up against a 4-3-3, I'll play 5 at the back with wing backs and generally have attacking midfielders.
These changes don't always work and it's no silver bullet. I have my fair share of frustrating results that makes no sense, but this approach generally works well.
*CAVEAT - Obviously it depends on the relative strength of both squads though, so no matter how well you prepare your starting tactic, a significantly better team will probably still be tough to play against.