Agreed.

However most often the handicap covers both options, so there is no edge.

Even if you find the edge ( which if you do , you gotta bet it ) , this is still a bet. So say a book gives 1/3 for a game that you are absolutely sure is 1/2. You must bet it, it is an edge and a HUGE one. Still , the true odds are 50-50 , so you might... lose! However on the long term you will be winning if you keep it that way.

What is the catch? They know. They never let the edge on the favorite, it is on the outsider. So you find the edge at a game that pays 1/20 while it is actually a 1/10. It is a HUGE opportunity, you must bet it if you are an edge chaser. It is a great bet, but the odds are still 1/10. You might lose 18 consecutive times at that bet, but when you win it you will get 20 back so you are a winner. The question is , can you afford to lose 18 times, or even 8 times?