If you've ever worked with Twitter's API, you should know that not honoring deletes on your app is against the TOS. It doesn't matter what accounts are being monitored, when a tweet is deleted by the account, you have to delete it from your server.
Now a situation like that where the moral thing is against the law would require us reexamining and changing the law. Whether it's whistleblower laws, minimum sentences or sentences for minor drug offences, these things all require a good hard look, and most likely, a degree of retroactive pardoning. But believing one's cause to supercede the law is a dangerous road to be on.
Now ToS are completely different. ToS are set by private entities, and as a single user you have little power over their content, only whether you accept them or not. They're an offer, not a democracy. I personally think that if you choose to knowingly violate the ToS of a service, then you should face the consequences of that regardless of the moral standing you may have. If you were using the Twitter API to defeat african warlords and Twitter decides that you're violating their ToS doing that and bans your account for it, well...you're SoL.
Not so fast, you can always use web scraping techniques as a defensive measure.
If your argument is "people don't have to follow the TOS because the TOS requires them to not comply with the law", that is simply wrong. If the TOS asks you to do something illegal in your country, it does not make the TOS illegal per-se. It means you can't use the service, because you can't comply with the TOS. There generally is no "well, i can do whatever i want and it's twitter's problem because i can't comply with the TOS". The fact that you can't comply for legal reasons is your problem, not the TOS's or Twitters.
INAL
There are 196 countries, so yes, you could say it varies. But i'm not sure which are the "plenty" you are thinking about, and i'd love to see specific examples of what you are thinking about.
Generally, most countries have pretty consistent law here. If the contract is a contract for you to perform something illegal (like murder), that will not be enforced. A contract that says "you must do X if you wish to use our service", in basically any reasonable country you can think of, is not going to be invalidated if you can't do X because it's illegal when done in very certain ways in very specific circumstances.
This is because, again, in general, you can't claim the benefit of the contract (using the service) but not have to have the burden.
IANAL, but here goes:
In The Netherlands certain clauses in TOS ('algemene voorwaarden') are void by default when they are against a limited list written down in basis contract law. Another list of clauses are null when they are not unreasonably limiting. So any contract within Dutch jurisdiction is limited in that way.
A contract with X.com would not hit Dutch jurisdiction directly, although with a Dutch website / translation and perhaps a Dutch office you easily come into reach.
Examples: You cannot be held to TOS that are not willfully handed to you. (So no tiny signs in stores, or hidden on websites. Exact translation obviously ambiguous.) Changes in pricing, especially early in the contract, usually give the right to cancel the contract. Should be able to cancel contracts anyways. Should deliver timely, and cannot contract 'untimely delivery'.
Still, daresay that contract law on the internet in the Netherlands is not a big field of litigation. For one thing, our damages are usually only 'true (financial) damages'. So in the context of (nearly) free products, you hardly get any litigation. Class action is limited, too.
Example here: consider a webshop that cancels your order after a discount gets too popular. You could probably demand fullfillment, since they could easily deliver from other retailers at a loss. But considering the costs of litigation are many times the difference in price, most people resign upon ordering elsewhere. Can't even say I regret that injustice, since the benefits of not clogging the judicial seem large enough.
Which is basically to say my understanding was that, in most countries, you can reasonably sign a legal contract and know you will never have to commit an illegal action in pursuit of it. And if your counterpart in the contract really wants you to commit an illegal action it's on them to decide whether they want to do business in a country where the action is it illegal. Not on you.
Once again, IANAL. And my understanding could be way wrong.
This is false :)
How does it square with your murder statement above?
But if you have an alternative, it's a valid contract for the legal alternative.
IE if i say "i'll pay you $1000, and you will deliver to me rice or smuggled opium", this is a valid contract to pay $1000 for rice. Also as i mentioned, you will generally be required to pay restitution. That is, pay back any benefit and least stop using/doing whatever benefit you are accruing(in this case, i presume using the service).
So you can't use it to your advantage.
Unilateral contracts are still contracts :)
(you can make some sane distinctions between licenses and contracts, but only in pretty simple cases, and twitters TOS is not a copyright license, but instead, an actual contract)
I mean to imply that most TOS are not binding, executed contracts.
There are some that overreach. I expect google/twitter/et al have written theirs carefully enough to not fall into this case.
Hypothetically, if Yahoo! automatically bans a suspected spammer account, and it turns out that the account was actually H.Clinton's official address, it shouldn't be Yahoo!'s fault for not knowing the legal identity of the owner -- rather, it should be the owner's responsibility to use the appropriate channels to conduct official communication, and stick to the ToS otherwise.
1) It is also against TOS to store tweets beyond a reasonable length of time.
2) Without the use of the streaming API, you do not have an efficient, automated way to track which tweets have been deleted.
2. Admittedly, that would be the most inconvenient part of the process. This would require regular scraping to validate what's been deleted and what hasn't.