Any weirdo you might meet online is the same one you might meet in person. It's not (where) you meet but (who) you meet that counts. Naturally their are some dating sites which have a higher caliber members than others. My advice would be to stay away from (FREE) dating sites and Craig's List...etc Like most things in life quality and dollar value tend to go hand in hand.
Use the same common sense you would in person when dealing with people online.
Don't rush to meet in person. Take your time getting to know a few people through the dating site's email prior to exchanging personal email addresses or phone numbers.
Remember the purpose of dating is to find out if you have enough in common with someone to determine if you want to have an exclusive relationship.
Too many people expect others to jump into a "monogamy state of mind" before they know each other. You don't look for a job sending out one resume at a time while waiting to see if the company will bother to contact you let along interview you. You may find the following hub to be of help with regard to online dating. A company interviews several candidates before selecting "Mr/Ms Right" for the job.
On a personal note I have been in relationships with women I met online that lasted up to 5 and 7 years. Online dating is just another modern tool for busy people to connect with one another. Just as a fork can be used to eat a salad or a slice of double fudge cake...etc You can't blame the tool for your experience. Each of us selects our own friends, lovers, and spouse.