Honestly not everyone in tumblr is into questionable stuff, like most stories that brake claim. Its mostly an image forum for people to blog about what they like and share pictures of what they enjoy. Its actually fairly similar to neogaf or pretty much any forum you have ever visited, the problem is that it got so big and so popular that its a place for all kinds of people to meet up, and that includes said questionable stuff.
When you join tumblr you can pick and choose what you want to see and who you want to follow, I'll argue its even safer than facebook in that its rare you are going to look at stuff you are not into.
Yeah, tumblr is pretty alright in my experience with it. I signed up for one back in 2014 to follow a few musicians and now follow about 700 different blogs. I mostly just reblog artsy pictures taken with "VSCO" filters, pretty chicks, music and occasionally anime.
Only downside is probably not being able to look at my tumblr feed in public because I have no idea if the next picture I'll scroll down to see is a cute puppy or some pornstar DP'd lol