Needless to say, this is a bad thing. That card has a very low balance and gets maxxed out pretty fast. It also pisses people off.
That's not to say that some issue or other you feel deeply about should be kept out of your writing - far from it. Just don't try to shove it in.
See, the things that matter most to you will find their way into your stories no matter what you do - or even if you're trying to keep them out. That's why all Pratchett (and all Hoyt and all Freer for that matter) has an underlying theme of 'what is 'human'?'. Or possibly 'what makes something a person?" I tend to hit the question of just where you find that hazy boundary between doing horrible things for the right reasons and doing them for reasons that just aren't sufficient justification - and how that affects the person who's doing the horrible things. And so on.
For that matter, if something happens that really gets under your skin, it will find a way into what you write. By then, the form could well have mutated to where no-one will recognize issue X, which is - trust me - a good thing.
Readers don't like getting lectured - or at least this reader doesn't. It tends to inspire immediate and rapid defenestration of the offending book. This is a problem, since kindles don't take well to that kind of treatment, and the delete key just isn't as satisfying.
Anyway, if I wanted a sermon, I'd go to church. If I wanted a lecture, I'd go to college. Besides, the issue of the week is old news by the time the book comes out, and the chances of it being back in that position when your book hits the shelves are pretty low. So many issues, so little time... I think they've got issue of the week booked through April 2057.
Another no-no with issues is to force your character to hand down the lecture - especially when it breaks the character. Whatever it is, trust it to leak out its own way. Having your main character stop, sometimes in the middle of the action (yes, there are Names who do this. They get away with it because they're Names - but I stopped buying their book when they started lecturing me), and sound off about issue X. Even, in the case of one formerly very popular author, when the character in question had no reason whatsoever to give a flying fornication about said issue.
(What does a flying fornication look like, anyway? I've often wondered about that... ahem. Sorry.)
I've mentioned some authors who handle assorted hot button or philosophical issues very well in their fiction. Anyone else?