Is theory really that necessary?

If 'theory' or 'opening theory' represents the correct way of playing a position then so be it. It's a matter of common sense. Just be sure you understand what you are doing. Blindly following the lines suggested by some experts from books or magazines without properly understanding the underlying reasons behind is a dangerous policy and may hinder your development. Chess is more than just rot learning. In my earlier days of the sport (from then to becoming a regional champion), I thought games are primarily won or lost by good opening preparation. Well, healthy opening preparation is important, but I underrate it considerably as compared to refining your technique in handling a specific position or honing your skill in calculating variations, at least at my current level in chess.com, and even if I go up to become 2200. Try to scan your database and play through ‘already resigned position from grandmaster’s games’ in your favorite computer engine and you will be enlightened. However, be sure to select only those games that might pose some challenge as you don’t want to make fool of your self playing through against a helpless opponent.

I learned much in theories. See my games. lol

Theory is a classic case of not having to re-invent the wheel every time you play. We have 100's of years of accumulated knowledge on Chess at our finger tips thanks to the internet so why not use it. It doesn't matter whether it's openings or end games its all there & being added to every day so why not use it. Yes you can learn it from your own games, mistakes & analysis but is your ability to do this better than Fischer & Botvinnik or the 100's of others who have already done it for us?

GM Yasser Seirawan made a very astute comment that its good to learn from your mistakes but if you can why not learn from the mistakes of others.

Just one last thing about getting hooked on informator symbols in Openings. I played a move in an opening that I wasn't totally familiar with that had a 'dubious' symbol next to it in MCO. I spent hours trying to work out what was wrong with the move, I couldn't see any immediate tactical opportunities for the other side, I wasn't giving up an out post square or control of an open file..Eventually I found the answer in a book dedicated to the opening in question - the move was 'dubious' because it allowed Black to exchange a pair of minor pieces in a slightly cramped position. I am sorry, but that level of thinking just isn't on the radar at my level no matter what 'theory' has to say!

That's news to me.

The point is not that you should memorize plenty of lines, but understand at least the general ideas in them. For instance, I have seen numerous players play this against me :

This just show they do not understand the idea behind Qc2, which is to play a3 without damaging the pawn structure. As a consequence, they just lose a tempo compared to regular Saemisch line.