Agree with Kev, what happens on linkedin is purely down to what users allow to happen, for example if you give it your email user name and password, it explains that it will search your email for addresses and try and use that to match to linkedin users who registered with the same address, and optionally invite those who it can't already match on linkedin. Who's fault is that, not theirs, always read on the page what its going to do with the information your provide.
Key think with linkedin to make it work is to ensure you know whoever you connect with well. I have close to 500 business connections and never get spam etc, ok the odd request to link from someone I don't know, just ignore it.
With regards to endorsing, if you list a skill, your connections have the opportunity to verify that you have that skill. As for creating company profiles, what's the fuss, all that information is available in the public domain, in the UK we have companies house, for free to the public I can see a company, when it was formed, who the directors are, where they live, which year they were born.
There are multiple issues here, main one being you need to take responsibility for the footprint you create in terms of personal information on the web, and be aware what gets listed. In the UK you can choose not to be in the phone book, not to have your voting address on the public list, register your company details at a holding address such as the accountant, register your domain address with the registrars address rather than your own, etc etc
Same is true with managing passwords on-line, I personally can't manage a different password for every site, so have tiers, so a very strong password for a couple of banking sites, then a strong one for anyone who I provide credit card details with, and then a lesser on for message boards etc, and also an email just for work, and then personal one for trusted sites and for order confirmations for on-line stuff, and then a one for the rest which I mainly ignore. Whenever you give out your email address, read all the checkboxes thoroughly in terms of agreeing where your contact details can be used. I get very little junk mail, cold calling etc