Danish Gambit

I think it is totally fine. Like most openings it is probably draw with perfect play.

What?

The Danish is an outstanding opening, however it is only suitable for a specific mindset Only a small minority of players are comfortable playing the kind of chess the Danish produces. Regardless of what advanced players or " engine peacocks " say, the Danish Gambit is not only sound, its what chess aspires to be. Engines don't play chess, humans do.

Isn't the Schlecter Defence (Queen exchange line) a simple way for Black to equalise and remove 90% of White's fun in the "full-fat" Danish?

If so, how does White really avoid it?

The Danish is very aggressive and simple

One of my friends, who's 1700 uscf, used it to nearly beat a 2280 uscf national master, and beat a 2130 rated national master. All of these are uscf ratings...they have chess.com ratings well in the 2300s to 2500s, so I think it is about how you play it. It's probably perfectly fine for anyone under high master level if you know typical patterns and moves.

It's probably a great opening at lower levels. I sometimes transpose to it when Black wastes a tempo with 3...h6 against the Italian.
The two major drawbacks are probably: 
1. Masters, who know what they are doing, might get an advantage with Black. 
2. It's fairly easy to decline without knowing any theory, for example with 3... d5, when the position is just equal.

Only with gambits does "equalize" transpose into "refute". The Schelecter isn't enjoyed by black or white, it is quite demanding for both sides. And it is true, gambits represent chess at its most simple and direct, it's the execution of gambits that is quite difficult.