Sorry a few more points.
Protected accounts. Obviously this is under the account holders control. It has pros and cons. Yes only followers see your tweets and when someone asks to follow you the opportunity to check their posting history is yours.
It also has the benefit of acting like a closed Facebook group. So if for example you wanted to target another user in a coordinated fashion it's a good base to plan that from.
That said, a lot of people protect their accounts simply to drown out the noise of the twittersphere as it were, no malicious intent whatsoever.
The downside of protection is that your tweets don't make it outside the bubble you've created which makes gaining more followers (if that's your intention) difficult.
I guess the think to be aware of is that many users have multiple accounts.
At an extreme they have one main account to publicise their point of view. A protected account to facilitate group private chat. Then multiple other troll accounts they can use to make complaints or to bait people. By bait I mean make an offensive/controversial tweet about their own cause in the hope people like/comment and then they pile in with their other accounts yelling bigot.
Other behaviour - which is particularly annoying - is when a user whose blocks you is altered (by someone else) to a tweet you've made they object to. They unblock you long enough to tweet as response them block again. The issue being that as the blocked user, you can't see what they've tweeted or know they've tweeted at all and thus have no right of reply. Your only hope is that someone else who is not blocked tweets you to it and screenshots the tweet so you can see and respond. I've seen Helen from Mermaids @mimmymum do this a few times.
I guess the upshot of what I'm saying is that if you know how it works and put the effort in Twitter can absolutely be manipulated to enhance your cause and work to silence your detractors.
If you have a relatively small following tbh it's unlikely your going to get much negative attention, but for bigger hitters it can be a real problem.