There is no such thing as inherent transitivity or intransitivity in Esperanto, but people often say there is because that's what's been taught. Transitivity is when a verb requires you to mention the item that the action is being inflicted upon, or not. For example, normally we say "I hate (something)", and simply going "I hate!" don't really make sense. But "I live!" makes total sense. Likewise, saying "I'm boiling (I'm sweltering)" is different from "I'm boiling water (I'm causing something to boil)". This is exactly what transitivity is.
Which verbs make sense with/without inflictees varies by language. This is where the problem comes in, in Esperanto. While the real the rule is simply to follow common sense and follow the -iĝ (becomes; sometimes "does to oneself") and -ig- (causes to be) meaning rules... it seems like most English-speakers were improperly instructed and never learnt these rules to begin with, then some weird idea was spread.
For example, "I eat the dog (I am eating the dog - Mi manĝas la hundon)". We don't need to say "eat-cause" because it's completely obvious. "I become-eat (to) the dog" usually doesn't make sense. (Mi manĝ(ig)as la hundon; mi manĝiĝas la hundon). Remember that -n is not just accusative case in general, but it can replace the use of prepositions when you're not sure which preposition to use - which means that sentence could mean "I become eaten at the dog" "I become eaten inside of the dog" etc. See, you'll almost never use those kinds of meanings with the verb "to eat", so that's why -ig- isn't necessary (but you CAN still add ig if you want! it's completely allowed and okay!!).
However "I red the dog (I am red the dog - Mi ruĝas la hundon)" makes little sense. It seems to mean "The dog thinks I'm red" or even "compared to the dog, I'm red".