Difference is though, on 4Chan the shitposting is usually at least funny and people don't tend to take themselves too seriously. (most of the time).
At worst, people are offensive or creepy, which isn't really that big of a deal.
On Tumblr though... not so much.
It has some of the most narcissistic and fun-sapping people I've ever come across. Which is annoying, because the website itself is really fun to use.