Vettel is nothing but a brat. I don't know what he was thinking to hit Hamilton intentionally.
However a line was drawn and that should be the end of it.
Frankly nonsense, if the line was drawn incorrectly by a few stewards on the day including what is in effect, temporary staff, and it doesn't reflect the line the FIA/teams in general/owners of F1 want then no, it shouldn't be the end of it.
That's like if one ref saw a player purposefully brake a guys leg in football, then punch the ref, but he chooses not to send him off because of some random reason... a bad decision doesn't just get completely ignored(truly bad) and the referee would likely be fired for letting that go. If the FA did nothing, said the decision was fine and kept the ref then that sets the benchmark for other referees. Obviously that wouldn't happen I'm making an extreme point to highlight it. FIA set the rules, if people on the day don't follow their directives and apply the rules incorrectly then why on earth should the decision stand?
Personally I think a deliberate hit is an auto black flag, and i think hitting anyone under a safety car without extremely good reason, is also something that should carry a hefty punishment.
I seem to recall Ham having a drive through a few years back(2013 maybe?) when he went like a foot over the white exit line on the pits, how can any unreasonable collision or deliberate collision under safety car end up with respectively, no penalty and only a stop/go in comparison.
IF it was wet conditions and Vettel aquaplaned into Hamilton.... even then, if the conditions were that bad being that close is pretty inexcusable but I could see no penalty, if Hamilton drives erratically it wouldn't be Vettel's fault and is already covered in the rules. The stewards forgot the first impact because they focused only on the second when usually the first would carry a punishment as well.
Also I'll go back to the whole, they punished vettel right after knowing Hamilton was losing ~30 seconds, we have no idea what they would have done if Hamilton didn't have that pitstop. They spent 35 or so minutes extremely reluctant to actually give Vettel the penalty which is a completely absurd and unreasonable amount of time to make such a decision, not least that with a red flag much of that time had nothing else to be considered at all and no racing to keep an eye on. Once Hamilton was going to drop 30 seconds it suddenly became easier to give Vettel a stop/go because it wouldn't effect the championship as much. Stewards giving out weak penalties and waiting to give them too long are things that shouldn't become standard just because they did it once.