> If you think [X], that's just your personal opinion.

<meta> You're saying "I don't trust your opinion" without any justification beyond asserting that personal opinions have low status. If you suspect Markus can't back his claims up, then ask him to. Also remember that if you hold a contrary opinion, then one of you two (possibly both) is necessarily wrong as a simple matter of fact. </meta>

When Markus said "there's something wrong with X", I guess he's actually saying "X does harm". In the case of Gmail, I'm inclined to believe that it does harm: better brain hacking (ads) through breaches of privacy —Google is effectively reading your mail. Also the "destroying the economy" effect may be quite real, though I think it's probably limited to short term damages.

> People are freely and willingly agree to […].

You're assuming people are rational. They're not. People freely and willingly agree to bamboozle themselves all the time, sometimes creating a network effect that will make it easier for more people to bamboozle themselves. Some people gamble too much and owe money to a Mafioso. Others join the Scientology. Or start doing drugs in a moment of weakness. Or use proprietary software, and eventually lose data. Etc, etc.

About the specific case of "cloud" centralized services (web mail, video streaming, blogs, social networks…), the main harm is a progressive loss of privacy, and increased dependence. I think it all stemmed from the thought that people are consumers, not creators. Technically this got translated by "people hardly need to upload". Hence the 'A' in "ADSL". Symmetry was sacrificed at the altar of download rate. Since then, any hope to have a decent server at home was basically crushed. Some providers even prevent you to host a server, or to send e-mail (they typically force you to go through their crappy, rate-limited relays).

Anyway, people did create. They wrote. They made videos. They shared their life with friends. And they continued to send e-mail. Well, the only practical solution to do all that was to use convenient centralized services. No way any given person would have enough bandwidth to host one's popular video. So it all goes to YouTube, creating a serious imbalance in the data transfer rates that makes some network operators uneasy.

Oh, there's an exception: Bit-torrent. It is an incredibly convenient and scalable way to share big files on the internet. And it's quite popular. Alas, because of asymmetric bandwidth, it doesn't work nearly as well as it should. Which is basically why we used MegaUpload —until "Big IP" shut it down. With symmetric bandwidth, it would have had no use, and Big IP couldn't have annoyed so many people.

We could have had symmetric bandwidth, convenient servers at home and all the privacy and independence that they can give us. However the market, people's preference for short term convenience, and network effects conspired against it. And the worse is, it works even if each individual choice is rational. Take the web mails: it could be rational for you to use it, but then, you participate in a network effect that get people to only accept email from the big players. This has already started: mails sent from home are often dismissed as spam right away. Most such mail is spam, but the (possibly rational) rejection is hurting the legitimate users.