If you've ever considered Disqus...
Cloud services do mainly two things: they offer some functionality and they host the data that is needed to do so.
Hosting data and providing services has to be paid and while some services directly take your money, other services sell the information they collect from you: they sell your private data.
Facebook is a great example for a company which makes millions by letting their customers run marketing campaigns against their users. If you want Facebook, you have to live with adverts. But you are not only target for campaigns, you are also feeding the monster with even more information.
But that is a fair deal: you have a direct benefit in form of a free service.
Disqus has been bought by a company (Zeta Global) that earns their money with the same principle: they run marketing campaigns for their customers against "their" users.
The big difference in comparison to services like Facebook is, that they are collecting data from people who do not know about that and do not have any benefit. Disqus is used on many blogs as an embedded commenting system. While the admin takes benefit from the service and thus might be okay with the "data against service" deal, the blog users do not know that their comments and mail addresses are directly fed into the mouth of a marketing company, making them marketing campaign targets.
If you want to be a fair admin and you want to stick to Disqus, you should at least inform your users that their personal info will be processed for marketing purposes.
But in my opinion, if you are a fair admin and want to have interaction even with those people who do not like to feed marketing companies, you should think about hosting your data yourself.