Can someone peer into my account without my consent?

No, it can only be done if you explicitly allow it, on a case-per-case basis. You must send the person/authority a viewkey file. For instance, if you run a charity, you would publish the viewkey along with some form of per-tx signature so regulators concerned with ensuring charities are run appropriately can peek into your books and see your accounts. Another use-case could be for a company to let its accountants, bookkeepers, and exco have visibility on the account and on the movement of funds. Or a married couple that want a shared account. Monero is private by default, transparent optional. The choice of whether privacy is relinquished for a particular wallet is the user's and the user's alone.

Unfortunately, for the moment, there is no tool to easily use the viewkey.

Of course, the said viewkey could be stolen or the person you trusted to keep it for itself could give it to someone else without your consent or even your knowledge.