Is it normal that i'm timid like a child?

Contrary to popular belief, it's not a good thing to be overly aggressive. "Tough guys" invariably end up either dead or in prison, and it serves their punk asses right. I'm sure Darwin would be rather proud too.

But while it's a great thing that you don't start fights, you do seem to be a bit on the passive side. A good rule of thumb is to never start trouble, but always be willing to reciprocate to it if and when the time comes.

I'm the same way. I just consider myself a pacifist because of it. :3

It all sounds normal to me.
Heroes are ordinary people made by extraordinary circumstances. Not by "teach(ing) oneself or condition(ing) oneself".
Just be yourself.

Yes. I explained I HAVE acted in a situation that needed it, as well have witnessed others doing the same, but these weren't "low risk". These were intense situations.

You described a desire to deal with obnoxious people. Which isn't necessary and not situations for 'heroism' and there's no need for you to get involved in them; someone being loud on a bus. That IS asking for a fight. Seeing someone get picked on or even harassed, is far different. It has nothing to do with normalcy, because a lot of people will ignore obnoxious people. It's no ones' place to step in, really.
Seeing something awful happening and standing by and watching, that would be being TOO passive of anyone, but even then you've explained no situation(s) where you've been needed, as help.

It is NOT normal to be so paranoid about things that haven't happened and probably won't.

When I was on the metro to a concert a few weeks ago, there was a pan-handler begging every single person for money and cigarettes (even after getting one person to give him a handful of ciggs) of course he was obnoxious, but we all gave a 'considerate' glance to each other-- understanding the next stop was soon and he'd get off. Although crowded, none of us needed to put ourselves in any compromising situation. None of us were cowardly for not stirring up a fight or getting verbal with him, it's knowing there's a time and place and it wasn't a threatening or even a bad situation. As I stated, even more recently I did get involved with the couple, when it WAS justified to do so. So there's a time and place and what you describe isn't justified fear. You just sound paranoid. Which isn't a good thing, because lose their lives to overly paranoid 'timid' people all the time. Being so paranoid, THAT isn't a normal or rational train of thought to have.

Well, you tend to say what's on your mind. Like most people, online it's easy and safe. You've rebutted every response thus far, with almost a defensive attitude, but moreso as if you already know the answer to your own question.

If what you mean by heroism; telling someone off for being loud or obnoxious on the bus, that's absolutely not heroism or the standard of. That's just being aggravated and wanting some form of macho attitude to defuse what's bothering you. That's more of a personal lament that leans towards you wanting to be the guy who can shut people up, tell someone to be quiet--if it's bothering you--and prove something to people around you. You used the term "yellow bellied cowards" and make it evident you feel like you're a coward yourself for not acting on these small situational things, just because it annoys you and you have to sit and deal with it (and not able say something)..
Most people have an innate sense of value for human life and WILL stand up against the wrong thing happening right in front of them. I've seen it numerous times, from petite girls in their early 20's taking on a huge "tough guy" at the bar/in other public places like grocery stores etc-- to a very skinny male knocking out a meat head who was verbally attacking his gfs and friends. Even personally getting involved (as recently as a week ago) when a man was yelling at his gf, parked at a local park, while she kept saying "stop" and was weeping in the driver side of the car. I didn't know the extent, but I knew to step in and ask HER if she was OK and attempt to defuse what was happening for her safety.

It doesn't take much to commit an act of 'heroism'. Big or small. It is more of being a GOOD person with good intentions. Heroism isn't saving the city, like batman and jumping buildings, like unfeasible movie situations. It's small tangible things in life that help others. Not strictly physical dominance.

What you describe sounds more like a lament that you're not more of a 'tough guy' in small and low risk situations and feel a lack of being respected and just want a form of acknowledgment and that respect. Taking classes to better 'defend' yourself, not describing even a need to, just appears like you want to be 'feared' and develop a physical element to portray a more intimidating exterior/feel more intimidating, to coincide with the feelings of inadequacy and cope better around crowds and deal with annoyances.

I've concluded that the best thing to do in this case would be to start attending a martial arts class, get proficient in the art of my choosing and build confidence because of it. Knowing that I would have little trouble beating up like 80% of anyone I met would definitely build up mine.

Either you challenge yourself to become a more aggressive guy, or you accept yourself as you are. BTW I bet you have more important things to do right? So why waste time seeking advice you already knew?
I suggest you forget about how timid you are and be whoever you wanna be.