I think it's only natural to be put off by that behavior. That's exactly why they have to try so many times, most girls are put off by that.

It's kind of like spam e-mail. When I look at my inbox (I'm too lazy to delete things) I have like 900 genuine e-mails. Yet I have 9,000 promotional emails I've never even glanced at. The majority of e-mail sent is spam e-mail. The majority of phonecalls made are telemarketing. True, it's just evidence of what kind of contact they are trying to make, they are probably only looking for a hookup, not anything personal.

IMO, don't waste your time on someone who treats you like you are a waste of their time. I don't use dating sites myself but I hear some women put a specific question or instruction in their profile to confirm whether guys that message them have actually read it. Seems like a good solution to me, if they don't respond to that, don't even have to bother reading their message.