Ssl – HTTPS doesn’t work anymore after adding SSLRequireSSL directive

The [R] flag on its own is a 302 redirection (Moved Temporarily). If you really want people using the HTTPS version of your site (hint: you do), then you should be using [R=301] for a permanent redirect:

RewriteEngine on
RewriteCond %{SERVER_PORT} !^443$
RewriteRule ^/(.*) https://%{HTTP_HOST}/$1 [NC,R=301,L] 

A 301 keeps all your google-fu and hard-earned pageranks intact. Make sure mod_rewrite is enabled:

a2enmod rewrite

To answer your exact question:

Is it bad to redirect http to https?

Hell no. It's very good.

TL;TR: you cannot serve both HTTP and HTTPS on the same port (443).

While it would be in theory possible to figure out based on the first data from the client if the client is sending a HTTP request (i.e. GET .. or similar) or is starting a TLS handshake (\x16\x03...) most web servers don't do this. Instead they expect the client to behave properly, that is use plain HTTP on one port (usually 80) and HTTPS on another port (usually 443).

Your URL of http://example.com:443 is causing the browser to make a plain HTTP request to port 443. But the server is expecting TLS there which means that your plain HTTP request is unexpected. Apache is at least nice enough to check if the incoming data for a plain HTTP request in this case so that it can offer you a more useful description:

Reason: You're speaking plain HTTP to an SSL-enabled server port. Instead use the HTTPS scheme to access this URL, please.

If you try such requests with other servers then they would either close the connection without any error at all or just hang because they are still hoping to get a TLS handshake from the client.