When you say...
...you're missing out on an important alternative: you can renegotiate. Publishers are not all mean, not all insane, not all bad businessman; some are actually none of the three. Many recognize that keeping talent happy is of value, and it's possible to cut a deal with them that gets you what you want.And if you did end up with a bad contract? You can suck it up; the terms were obviously good enough for you once.
Sometimes all it takes is to ask. Other times, you ask and you offer something of value to the publisher. "I'll finish the three issues I promised at this page rate, but if you up the page rate 20%, I'm willing to do six." "If you give me back my movie rights on Cute Li'l Mutton Girl, I'll do two work-for-hire issues of Captain Fistguy for you."
I've been on both sides of this. Heck, earlier this year, I got back the rights to a graphic novel script I'd written years ago, which the publisher had a few false starts with and then went nowhere on. They'd paid for the script (a cheap rate, mind you, but the checks cleared). I presented a minor argument of why they were theoretically in violation of contract, as they'd represented royalties as part of the pay and as there was no publication, there was no royalties... but really, it was just a short letter, and they responded by releasing the rights (and they had grabbed 'em all) to me, free and clear. (Of course, had they found active Hollywood interest in the script, I might not have been able to pull it off, but it wasn't an impossibility.)
You're right that by far the best time to fuss about a bad contract is before you sign it. But in the long run, freelancers should remember that they're businessfolk, the publishers are businessfolk, and making deals is what businessfolk do.