[TLF] recognizes a transitive direct usage of the verb vouloir, as well as a transitive indirect usage (with "de"). The transitive indirect form is given as more usually used in negative sentences.
There are "easy" cases where de indicates a part of only:
Je veux la soupe. (all of it)
Je veux de la soupe. (some of it will be enough)
In this case, the difference in meaning justifies the use of de. If you don't want the whole soup, but only some of it, you have to use de.
There are also many cases of negations where de is required:
Je ne veux pas de lui dans mon équipe.
Je ne veux pas lui dans mon équipe. (incorrect)
Je ne le veux pas dans mon équipe. (mandatory if not using de)
Je n'en veux pas dan mon équipe. (most commonly used?)
But is de always required in negations?
Let's try the pair:
Je ne veux pas de cette voiture.
Je ne veux pas cette voiture.
where the car is not divisible in parts like soup. In this case, it is hard to perceive any real difference in meaning, and it seems that de can be included or left out. The meaning does not seem to drive the usage of de. there is a given car. You don't want it. There is not much more going on here.
In the example posted by the OP, where IMHO both forms are possible:
Je ne veux pas d'un amour sans faille.
Je ne veux pas un amour sans faille.
I cannot feel much difference in meaning either. The first sentence flows better than the second one, maybe. But these two sentences actually say the exact same thing, so here again, meaning does not seem to be the driver for the usage of de. Let's take another example:
Je ne veux pas ton amour.
Je ne veux pas de ton amour.
It is again hard to pinpoint the actual difference between these two sentences. The first one maybe feels more direct, and therefore stronger (?), but that is IMHO questionable. You can also make a case that in the second version, you only want part of the love the person, but that does not feel like it is necessarily the case.
Le parti ne veut pas de Poincaré à l'Élysée (Aragon, Beaux quart., 1936, p. 203)
Is that de required? No:
Le parti ne veut pas Poincaré à l'Élysée.
has the same meaning in the end, except maybe that this last sentence is more direct. The first one also feels more natural. The second one is IMHO grammatically correct. The meaning is the same.
Vouloir de Mlle X pour épouse (Caput 1969).
Is there anything wrong or different if we remove that de?
Vouloir Mlle X pour épouse.
Not really. Here, using de might be more idiomatic. But retracting that de does not materially change the meaning of the sentence.
So, from these examples, beyond cases of divisibles things and negations where it is required, there is number of cases where it does not look like the addition or removal of de makes much difference at all. The choice of using de or not would not always be driven by the meaning of the sentence.
In conclusion, de is required to indicate that you want only a part of the thing you want, there are many cases of negations where de is grammatically required (but maybe not all), and then there are many cases (of negations) where it makes very little difference in meaning, except that inserting de feels more natural.