†This is where logic or mathematics operates differently from human language (aka natural language). Strictly speaking and mathematically speaking,
1. "N is Y, if not Z" would be read as
2. "if N is not Z, then N is Y".
However, in many human languages, English included, saying 1 doesn't mean just 2. To understand this, we should think a little about the motive of a speaker who said 1.
Quite likely, the speaker's intention was
3. "If N is not so great as Z (or any quantity > Y), it is = Y"‡.
But to say 3 exactly in those words would be clumsy,
and thus the speaker would naturally rephrase 3 as:
4. "N = Y if N ≠ Z",
or in plain English: 5. "N is Y, if not Z".
We can try another approach to show that if not can be used to mean perhaps even.
Let N is the number of people who has an attribute Q.
Consider these two following propositions:
(a) N is Y, if not Z.†
(b) N is Y, perhaps even Z.
Let Na is the set of all possible values of N for proposition (a).
It is easy to see that Na = {Y, Y+1, Y+2, Y+3, ..., Z}.
Let Nb is the set of all possible values of N for proposition (b).
It is also easy to see that Nb = {Y, Y+1, Y+2, Y+3, ..., Z}.
Now, it is clear that Na and Nb are equal. Hence, (a) and (b) are equivalent.
Thus, if not can be used to mean perhaps even.
Q.E.D.
Someone who is self-indulgent gives themselves a lot of treats.As a synonym,it also means
spoiling yourself
to spoil means "to treat someone very well, esp. by being too generous"
or
pampering yourself
to pamper means "to treat with too much kindness and attention"
As a broader definition "An indulgent person would be a person that is self-consumed; maybe talks about themselves and their stuff and they don't really listen or are interested in others' lives, events or things; everything is about the self-indulgent person."
Best Answer
This is an interesting question because I think it's going to hit a bias in ELL.SE user demographics.
The expression to blow the whistle means to expose corruption, that is, conspiracy or extortion by means of state power or state-backed corporate power.
So what you feel about whistleblowers has an awful lot to do with how you feel about state power.
ELL.SE users draw very heavily from the tech trades, and, at least in the US, that is a population that tends toward having negative feelings about state power, or who are at least very touchy about how state power is used. I count myself in this cohort. On top of that, the Snowden revelations have primed a lot of people already skeptical about abuses of power to feel very negatively indeed about it. Among this population whistle blowing is seen as something heroic.
It can be hard for those of us in this demographic to realize there is also a sizable demographic in the US which is very authoritarian in both personality and culture. They actually think authority and systems of authority are good things, and that people who challenge authority are immoral. For them whistleblower is a negative term and blowing the whistle means something very like betrayal. At best, if a whistleblower is vindicated subsequently, people with such sympathies to authority tend to see the whistleblower as, at best, a "necessary evil", and someone of low character who happened to be right -- like a criminal who turned on other criminals. These are the people saying, "Even if Snowden was right, he had no right to do what he did."
(This is sort of off topic, but if you're interested in this sort of thing in US culture, you may want to check on The Authoritarians by Altmeyer, "Red Family, Blue Family" by Muder, Red Families v. Blue Families by Cahn and Carbone, and the work of Jonathan Haidt on morality across cultures (somebody else's paraphrase here, his TED talk here)).
As to the valence of blow the whistle in any other English-speaking culture, I can't speak.