Of course it is. If other peoples' votes weren't our business, nobody would campaign or try to convince people how to vote. And if you're going to say that it would be much better for conservatism if Obama won, then it is perfectly legitimate for others to point out that the logical conclusion of your position is for conservatives to vote for Obama, thereby advancing the cause of conservatism.
If you don't have a rebuttal to that argument, I'd suggest you check your premises.
I wouldn’t presume to “tell” another how to vote; a write in ballot is always perfectly acceptable, however.
Any logician should be able to clearly perceive that a Republican Congress with a Romney presidency is more damaging to the Conservative Cause than ANY alternative in the White House.