Here's a question: What do you guys consider spaming, and do you find that cheap?
"Spamming" a move is simply using the same move over and over without thought, think someone simply throwing fireballs at the opponent without any rhyme or reason. The definition has been blurred on a casual and competitive level as of recently, I think, often being thrown around when people are seen using a defensive playstyle that includes the use of fireballs or far-reaching moves.
For example:
Spamming is Ryu throwing a Hadoken at full screen regardless of the opponent's advancement. He is simply sitting in the corner, no movement to be found, as he chucks fire at you, regardless if it's achieving anything or not.
Keepaway is a character like Morrigan in UMVC3: she has multiple fireballs and flight patterns that require a good amount of forethought and reactions to apply correctly in a match against a player of equal skill level. (If you're unsure of what I'm referencing, or just want a better visual, look up Chris G on YouTube, he's considered one of the best UMVC3 players and uses Morrigan.)
While the two appear to be achieving the same goal, the former case is fairly thoughtless, basic, non-changing, and overall not good at all. An intelligent player will be able to wait out the spamming Ryu, eventually getting his way into a favorable position due to his predictability. The latter is much more difficult to deal with: the Morrigan player is thinking ahead of the game, and in the game at the same time. He's fighting just like a rushdown character would, but with a different character that functions in a much more different way.
Obviously, this small scenario is not all-encompassing. People spam moves that aren't long range, such as throws, fast jabs, or other longer range moves (think Dhalsim's punches and kicks in Street Fighter). The result of which is the same, however; spamming is predictable at its core. It's simply repitition that can be read and counteracted given a clear head and some careful play.
As for your second question, no I don't find spamming to be broken. It simply makes players play more patiently against spammers. To me, it's almost like playing on lower ladder, you're gonna wanna play a little more conservatively and be more careful (referencing the varying skill levels of low ladder players, etc.), but it's certainly not unbeatable.
Tl;dr: Spam is thoughtless mashing and repetitive use of the same move(s), and is often misused as a term for keepaway play. It is not broken, it just simply forces the player to play more patiently.
