There are, however, somethings that you should never do, never think of doing or let get out of the gate.
Who in the world thought that a CG Garfield interacting with live actors could possibly produce anything of quality? And Namor the Sumariner as a movie? Why is Jurrasic Park 4 even being seriously considered? And don't get me started on that piece of trash Superman script that has Lex Luthor as a Mulder-like FBI agent and then revealing that he's a Kyrptonian too.
Another thing, just because a movie makes $50 million in its first week, that does not mean that it should automatically get a sequel. Especially if the next weeks box office has it drop over 40% into the next week. That is just wrong. Sometimes you can hype and spin things so that they look excellent but after we see them we know them for the crap they are and we tell our friends.
Every once in awhile everyone needs a cheezy movie and I understand that however, there only really needs to be one or two of them a year. For me Tomb Raider 2, Charlies Angels 2 and The League of Extrordinary Gentlemen really filled the bill. Entirely. There doesn't need to be any more this year. At all. Dumb and Dumberer never needed to exist at all.
So, to sum up:
Pirates of the Caribbean = Good. Legally Blonde 2 = Bad.
Lord of the Rings = Good. From Justin to Kelly = Bad.
X2 = Good. Dirty Dancing: Havana Nights = Bad.
Troy and Van Helsing = Good. Scooby-Doo 2: Monsters Unleashed = Bad.
Thank you for your time.