Your blog is for you to share - at your discretion - with the world, with your friends, or with one special friend. You make this choice using the Settings - Permissions wizard. If you restrict access to your blog, simply so you can actively meter your readers, you can setup alternate access procedures, and let strangers request access.
If you don't want strangers accessing your blog, and you have planned access restriction properly, you can block public access to your blog. Period.
This coin, like many others, has two sides. If you have been enjoying access to a blog, and the blog owner chooses to make it private (as discussed above), maybe you can find a way to contact the owner and request access, so you can continue to enjoy that blog.
If the blog owner does not want you to access the blog, he / she can ignore your requests. If the blog owner really doesn't want you to access the blog, she / he probably won't even provide an alternate access procedure. Some blogs are by permission only, and only if you already know how to request access. If you don't know the owner, or a designated reader, you won't be able to request access.
Don't count on Blogger to contact the owner on your behalf, and don't post in Blogger Help Forum, and waste time while you whine about loss of access.
Find another blog to read, you can't read that one.