1. "I don't want to clog up the dash."
Fair. That's why there's a queue. Use it so your posts are spaced out and you're not clogging anything. (And if you do clog someone's dash because your hourly posts are too many, then that's on that person for not following more people.)
2. "It's so weird, I don't want anyone to know I like it."
Hello, you are on the cringe website, we all like weird shit, that's why we're here? If others don't like it, they can scroll past it. (Also they probably like it and just aren't telling you.)
3. "None of my followers have followed me for this content."
Then use a tag and tell them to block the tag. It's your blog, not theirs, put up what you want. Again, cringe website; please see #2.
4. "I haven't read/watched (this fic/article/book/movie/TV show) yet. What if it's terrible?"
So? Say it looks interesting and you'll look at it later. And maybe it'll be terrible to you, fine. But it also might be someone else's favorite fic/article/book/movie/TV show ever that they discovered through you.
5. "They don't reblog my stuff!"
Yeah, probably they're saying the same about you. Vicious cycle. Maybe be the one to break it? (Or maybe they don't reblog yours because they didn't see it because no one else reblogged it either. Please see #4.)
6. "I only get three reblogs a day and after that I am not allowed to reblog anything else for a full 24 hours."
Okay, now you're just making shit up.
7. "My reblog queue is already full."
You know you can make that go as fast as you want, right? Also if you're reblogging that much, you don't need this post. Go watch one of those shows from #4.
8. "No one follows me, no one will care, everyone has seen it already."
Maybe no one follows you now, but that won't always be true. Part of the reason you reblog is so that people can find you, and use what you've reblogged before to decide if they want to follow you now. The OP will care if you reblog their stuff; you'll make their day by doing so, and maybe they'll follow you too.
Tumblr moves fast, and there's always newbies. There is always something someone hasn't seen. Be the one to show them, and turn them into today's Lucky 10,000.
9. "I don't want to spam reblog from just one person!"
Yeah, this isn't Insta or Twitter or whatever, doing this is a compliment, honestly. Use your queue if you're that worried, though (see #1).
9. "I guess I just didn't think it mattered."
Sometimes we all have quiet days. I can't claim I reblog absolutely everything I should, either.
We say we want community; we say we want connection; we say we want to be part of something bigger.
This is the best, easiest way to do that.
If you like it, reblog it. If you think someone else might like it, reblog it. Participate. Build the community you want.