If it is, then an awful lot of vanilla people are engaging in "rape".
Think of it this way: Ticklephiles are probably the only ones who participate in "consensual planned tickling", such as with bondage, the tickle gatherings, safewords, etc. Most vanilla husbands who tickle their wives usually dont go up to them, and say "Honey, can I tickle you?" The tickling just happens.
That having been said, the type of tickling also plays into this. Brief, playful tickling of feet, or sides, etc, for short periods of time, is harmless, but, if one is talking about holding down their partner for a long period of time, and.. tickling them until they feel pain, or cant breathe, etc, against the partner's will, then, that at the very least, is abuse.
There is a fine line.. but.. this is at least how I see it.
Mitch