Well, if you look at it from a general point of view, then yes, most
crackers (not hackers

) fall into that category. But I wouldn't call most of them crackers in the usual sense of the word.
When we talk about computer crackers, we (or I, at least) usually think of someone with vast knowledge about computer security and computer systems.
As Marie B. said, most of those guys are just "script kiddies" who know nothing more than to look for pre-made exploit scripts that give them access to websites, which they promptly deface, leaving messages that proclaim their "l33t sk1llz"... elite skills that they really don't have, because they have absolutely no idea of what happened when they cracked into the website, they only know how to execute that script and mess up the website.
If someone asked them what was going on in the background, what exactly that script was doing and if they could recreate what the script does, using other tools, etc... they wouldn't even have a clue about how to make up an excuse for not knowing anything about that.
For their lack of knowledge and misuse/abuse of tools created by others (exploit scripts are usually created by security experts for the purpose of testing their systems for vulnerabilities and they usually share those tools with the community) for a maliciouse purpose, I don't grant them the title of crackers.
They're not even hackers, because not only they don't know anything about computer security, they didn't even modify/hack anything to make it work in a way they wanted - they simply used tools created by someone else.
Hence the term "script kiddies"

In the end, yes, there are also those who do know their share of computer security and still use it for stupid/malicious purposes. But I wouldn't say those are the majority. I think the majority are those script kiddies mentioned above.
PS - it's good to have some time to come to the forums again, now that college exams are over!