Manga aggregation is pretty much by nature a morally grey area, by extension of manga scanlation itself. You take illegally replicated materials, and distribute them on the net for free. The only reason scanlation gets by legally is because the content publishers have neither the resources to consistently pursue and prosecute scanlators, nor often to distribute the material themselves (in the first place). That's why, from a fan/moral perspective, scanlation is about making it possible to enjoy/appreciate a series/part of a medium which would otherwise not at all be available.
The problem with aggregators is that it's pretty much impossible to think of hosting an undifferentiated mass of manga scanlations without some sort of income stream. However, the fact that it is possible to host an aggregator site based on just ad revenues (since with scanlated manga you pretty much don't need to deal with stuff like translation, licensing fees) means that it will be mostly profit-minded parties which do it. Once you step past the line of merely distributing translated unlicensed materials which the original publishers are unable to provide in your language, to outright profiting from the illegal distribution of those materials, what you do no longer has anything to do with "fandom" but is simply (intellectual property) theft.
In an ideal world scanlation would be uniformly small, fan-driven, and non-profit in support of smaller/lesser-known properties, while larger properties which could conceivably manage to sustain an income stream would be distributed by legal internet distribution services. However, that isn't the case right now, which is why scanlation aggregators (and also a number of unscrupulous scanlators influenced/supported by them) exist. To the extent that aggregators provide a convenient (if frequently low-quality) method for maintaining exposure to a lot of manga material, there isn't much of an alternative. However, what fans can do is do their best to support legal distribution of manga (etc.) wherever possible. In regards to scanlation, correspondingly, that also means doing one's best not to support a culture of illegally profiting from other people's work.
