Indeed. If tactical voting reduces the Tory majority to zero, or makes them a minority government, they have a) no overwhelming public mandate and b) no way to ram oppressive or divisive legislation through Parliament. Ideally, the other parties join in alliances and coalitions of opposition, but even if they don't co-ordinate the Tory party would not have the carte blanche it currently enjoys, to make hay while simultaneously undermining our rights and freedoms.
We have learned in recent years that majority government is often bad government. Let's warm to the concept of minority or coalition government. It is after all, in a fundamental sense, considerably more democratic.